I bought this unit and in the beginning it worked really well. Then the on-off valve started to fail. The ON worked but the OFF had to be manipulated to close every time. This progressed downward until it would never shut off. The valve is made of plastic with several "O" rings, and the mechanism to open / close is controlled by a plastic handle. It's simple and should work, but it doesn't. *** DON'T BUY !***

PS - I used it twice a year for 3 years and took great care to wash it and let it dry before storing

I did a LOT of research before I took a gamble on this product. IM GLAD I TOOK THE GAMBLE. Like most things on amazon, if you read and follow the instructions, you will be fine. The product works better than advertised. I do enjoy the fact that it came with something to strap to you back instead of carrying it, pumping then spraying, and moving (repeat). Back straps was a great addition to the design. Also, being quasi-see through helps A TON when guessing how much spray is left. The product came with 2 different spray nozzles (both remarkably easy to install). I chose to use the wide jet. OMG. Best idea ever. Im used to using the handheld Ortho perimeter spray stuff. Its great stuff but takes a long to treat my property and garage. So I bought this machine and transfered the the Ortho into it and PROBLEM SOLVED. I was able to do the entire property (including porch and garage) in a 3rd of the time. The wide spray jet was just PERFECT. Im sorry if this review seems like im bouncing from thought to thought but I am at work on a break and trying to leave my honest review.

I bought this in February but waited until basically the growing year was over to leave this review. So far so good as far as working properly. I was pleased that it never gave me a problem. No leaks, no clogs, and no problems pumping. I was diligent to clean it well after use and I only used weed killer during the year. I haven't tried anything else so can't say how that would be. For my use it worked great. My only issue would be the fact that you have to pump it up quite often but, I expect that with any pump unit. At least it's easy to do.

I can't say anything about "wearing" the backpack because I used a golf cart to carry it strapped down to the seat. It was fairly easy to just reach over and pump the unit and spray as I moved. I will say that the unit is probably not "comfortable" to wear at all plus, it's very heavy, as you would expect with 4 gallons of liquid in there. I did put it on once just to see what it felt like and I didn't even have it full. It's not only heavy but also awkward trying to put in on your back. For me personally, I don't think I would want to wear it for any length of time when it's filled to capacity unless you could adapt some better, more comfortable straps (and a sky hook). I'm thinking of doing away with the straps altogether just because they're in my way and I doubt I'll ever carry it around on my back.

I've used the cheap 2 gallon sprayers my entire life and this is the first "upgrade" to that. I can't compare it to other more expensive units since I've never owned one but, this is great compared to the cheap ones. For the money, it's well worth it. I recommend it.

As others have said, I SO wish I'd bought one of these a long time ago, especially last year and during all of this year. I put it to use for the first time today (8-3-2017) and, other than the difficulty I had getting it onto my back, I was very pleased with all of the features and construction of the sprayer. The pump is effortless, there is no leaking anywhere, and the amount of material that the large spray hose provides is wonderful. Other than me being a 68 year old weakling, I'm happy to recommend it to you if you have to spray three or more gallons per session. It was actually physically less uncomfortable than toting a one gallon sprayer, which always causes a lower back spasm after about and hour.

Wow, this thing is great.
I have a little 0.3 acre suburban lot & keep it nicely manicured & maintained. And try to keep it aphid & mosquito free.

This sprayer, used with insect control concentrate, works great. Only 2 ounces of concentrate in 3gal of water covers my entire yard with a light mist and has reduced the outdoor nasties 90% or better. this is the concentrate: https://www.amazon.com/dp/B00ARKSBEA/ref=cm_cr_ryp_prd_ttl_sol_11

The sprayer is thoughtfully designed and works very well. I'e had it only a couple months so we'll see how it holds up, but so far, so good!