I had some small specks which were evident on day sky shots when magnified to the max. Since my Nikon D600 has a new shutter (replaced under warranty because of the oil splatter issue), I assumed it was dust. With the mirror up, using a small LED flashlight, I could see dust on the glass cover plate which protects the sensor. A hand-held blower (not canned air) remove most of it, but some was still evident (I photographed a white interior door to check). I used the wipes and first dragged it from left to right, then flipping the wipe over, I dragged from right to left (as the directions instructed). The dust on the glass cover plate was completely gone (nothing visible with the flashlight or in a subsequent picture check). It makes one nervous, but in reflecting, the plate is glass (so very hard) and you are dragging the wipe across the glass and not grinding any dirt into the glass. With reasonable care, one should be fine.

When you got a dirty sensor, you cannot see it with naked eyes.
You need a lupe and a flashlight to barely see them.
I was somewhat skeptical, but these do work.
I also recommend that you get a Giottos Rocket blaster to remove any loose particles on the lens or inside the camera.
I DO NOT recommend compressed air of any kind, ever.
There are plenty of good tutorials on Youtube regarding how to clean your sensor.
You should use the right size for crop sensor and full-frame sensor as the swabs are designed to fit each types.

This kit is good as any I have seen that are more expensive, not that these all that cheap for what you get.
I like using two of these, first one wet, with provided solution, then 2nd pass with a dry one.
Using gentle but firm pressure, whereby the plastic handle bends slightly as you press against the sensor,
you make one pass each way, using one side, then the other side going opposite way.
Then, I follow through same way with the 2nd dry swab, one pass.
It seems like a waste to chuck'em after one use but these are not reusable.

I recycle the used ones to clean particularly dirty lens or filter.

https://www.amazon.com/Giottos-AA1910-Medium-Rocket-Blaster/dp/B000L9OIQC/ref=sr_1_2?ie=UTF8&qid=1486478286&sr=8-2&keywords=rocket+air+blaster+camera

I've been plagued with a few spots on my photos, with my Nikon D800, when using a high f/stop which is pretty typical indication of a dirty sensor. I have a local camera shop that will do the cleaning for about $60 which I don't think is unreasonable. I just don't want to be without my camera for a few days. After reading the positive reviews I figured I'd give this kit a go. I was a little nervous to do it but honestly, it's pretty simple. It only took a few minutes and the results were very good. No more spots and I only used two swabs, one with solution and one without. I used a flashlight to get a good view of the sensor. I could see the specs that were causing the issue and after the swabbing everything was gone. I like this kit so much I've ordered some swabs for my D300 which has the 3/4 sensor. I tried to use these swabs but they are too big. I ordered these instead, without the fluid since this kit has plenty VSGO Professional Camera Sensor Cleaning Kit APS-C DSLR Sensor Cleaning Swabs For SLR Digital Cameras Cleaning

No matter how many good comments and 5 stars, I was still skeptical of using it since a camera sensor is just that delicate. But nope. It worked flawlessly on my Sony A7s sensor. Stains which looked like they had dried up and had no way to be cleaned except for a wet cleaning, this kit was the answer. Just 2 drops on the swab and I waited couple of seconds for it to soak in, and in 2 wipes, Sensor is as reflective as a mirror spotlessly clean.

Just make sure you don't use more than a drop or two, else the sensor will get those droplets. Also, after you clean the sensor, you can re-use the same swab to clean your camera LCD display. Although not recommended, It didn't hurt my LCD screen at all. Rather, I just got a dust free clean display.

These are good sensor swabs at the right price. I have cleaned DSLR sensors for the past dozen years, and had prior to used Photographic Solutions swabs. Now I use a combination of CRC Duster, Arctic Butterfly (recommended), Eclipse cleaning solution (recommended) and these VSGO swabs. For dust only I use and recommend an Arctic Butterfly and also use the CRC Duster. The trouble is that sensor dust gets sticky and becomes difficult to remove, and it can take a half-dozen repetitions to get a sensor clean - so it's nice that these swabs are cheap.

The process goes like this: First I blow away dust from the camera exterior, and wipe the area around the lens mount with Photographic Solutions Pec Pads (also a must-have for camera and lens cleaning). Using canned air is fraught with peril and not recommended for anyone without mechanical aptitude and unaccustomed to risk. First, the majority of canned air has "bitterant" to prevent teenagers from using it to get high, and the CRC brand is the only one I'm aware of that does not contain bitterant, which leaves a residue (check the fine print on the can label). Second, using canned air involved a risk of getting freezing liquid on the sensor... so you have to have your brain engaged... store the can only in an upright position, never tilt it or the freezing liquid might be expelled and before applying it to the camera do a test spray onto your hand to make sure the flow line is free from liquid. Assume that if you spray freezing liquid onto your camera sensor then your camera is ruined, so that's why you'll never read elsewhere about using canned air. However, it effectively removes large dust particles from the DSLR mirror box, focusing screen and finally, sensor. I prefer to remove the big particles without using swabs to keep them from scratching.

Next step is to use the static brush of the Arctic Butterfly to further remove dust from the sensor. I should remember to pack the Arctic Butterfly for travel to use after trips down dusty roads choked with diesel exhaust. Still, I'd only expose the sensor for cleaning in a clean environment. The Arctic Butterfly might do 90% of the job.

Using the sensor swabs, I use one or two drops of cleaner to wet the swab, and try to swipe in a complete stroke without picking up the swab. I have tried the cleaning solution provided with these VSGO swabs, and it appears to contain water which when dries can leave streaks or "water-stains" on the sensor. Instead, I think Eclipse from Photographic Solutions dries cleaner, and a 2 oz bottle is a lifetime supply. Using one or two drops of solution is key to minimize the amount of solution that must evaporate.

A next key is to check for dust effecitvely. Do to this, use a lens that stops down to a very small aperture, like f/22. I shoot into a blank white computer screen, using a word processor with blank page, shooting RAW and using the base ISO of the camera (in my camera's case that's ISO 100). No need to go outside and works in the dead of night. Also, I set the exposure compensation to over, like 1.5 or 1.7 stops.... else the exposure of your blank white computer screen will result in a medium gray. Next, import this image into your RAW processor, and set contrast and clarity to maximum, and shadows and blacks to minimum. What first imported looking clean now probably looks dirty and streaked. I find that I have to go back up to a half-dozen times and sometimes almost scrub the sensor. Each time I either use a new swab or use the canned air to thoroughly blow all the dust off a use swab. I'll finish up with a final pass using a brand new swab and a minimum amount of cleaning fluid, trying to make a full, continuous sweep of the sensor so I only pick the swab up off the sensor once at the end of the stroke.

Getting the sensor really clean is takes patience, is finicky and requires a level of retentativeness. But clean means clean, and it's nice that these swabs are cheap so the cost component of the job is one less thing to worry about... You might not want/need to use f/22 any other time!