I've been using the wired version of TENS units for a couple years. At least, I have used them when I was at home and didn't have to move much. I used them at night, but that could be chancy. The wrong move pulled the plug off the pad and I woke up to the equivalent of a yellow jacket sting. This unit is a pricy thing, so I had some reservations. And, there are a lot of negative reviews. I've used these wireless ones for a couple of days and can report on everything but how long the pads last. So far, so good on that, but we'll see. Otherwise, I've been very happy. They have worked well over a couple of nights. The first night, I hadn't changed the channel on one of them and that was problematical. Different spots need different intensities. After changing the channel on one so that I could have different intensities, they worked well. One charge lastex the night with no problem. Today, I wore them to my physical therapy session. So I drove with them, did my physical therapy with them, and then went to a store afterwards. I had no problem with them coming off or stinging as TENS will when the pads shift. They stayed stuck throughout all that. I saw a one-star review where someone complained that when he tried to put the pad on his back, it took contortions while he tried to look in a mirror to turn the pad on. There is a simple solution to that. Turn the remote on and turn the pad on and set the intensity to zero. If you do that, your fingers won't get stung. Then put the pad on your back, which isn't hard to do, and then increase the intensity. So many of these negative reviews seemed to be something like that. I suspect I will spend more on pads than I would like based on my experience with the wired versions, but the portability of these things will make that worth it. I'd rather spend money on that and give up a couple of pizzas a month.

Better than the chiropractor office. Good for lower back pain. No batteries to use . Rechargeable with the plugs provided. But will only charge 2 things at once. But not a problem. Satisfied with this product

I recently received this wireless unit. Unlike the other reviews so far, I wanted it primarily for the EMS mode. It is a highly rated unit but there are a couple things you should know before you buy it.

Pros:
-Incredibly versatile! You can customize the stim so many ways to fit your needs. The stim levels go so high, it is unlikely you will ever need the highest.
-It comes with a manual that is thorough and easy to read. Read it through once and you have it.
-Works exactly as advertised.
-The wireless version is worth every extra dollar. No wires, very discrete. Wear the receivers under your clothes and toss the control unit in your pocket or purse.

Cons:
It can be almost impossible to snap the electrode pads to the receivers! You may have to put the pad and receiver on the floor and push with all your weight through your heel many times. One snap was so impossible, I almost sent the whole thing back after 30 minutes of trying to get the pad to snap into the receiver unit. It finally gave way and I hope it loosens up.
-The manual says the electrode pads only last for 20-30 uses. So before you buy this, make sure you know the investment continues. Four more pads costs $30 and you can go through 20 uses very fast. These pads aren't sold on Amazon right now but at the moment, the U. S. gets free shipping from the manufacturer.
-It comes with a nifty carrying case in which the control unit and charger fit but, oddly, the receivers don't fit with the pads attached. I guess that's what baggies are for.

So if you are willing to overlook a couple of quirks and if your wallet can afford the continuing investment you really get your money's worth out of this product.

UPDATE:
Just an update on the company's "20-30" uses of the electrode pads before needing replacement - I have used the pads significantly more than 30 times and they are still going strong. The key is that after use, be sure to put the plastic shield back on the pads and smooth out any air pockets. This way they don't dry out.
Also, they have just come out with channel 3 and 4 receiver units. If you have a lot of pain spots on your body, you can have 4 of these babies going at once. Just be sure you order the electrode pads with the receivers because they don't come with them. Just a tip - after you set your program and start the stim, turn off the hand-held control unit to save battery.
They don't have a "dollar electrode club" for the pads yet, as they do for the smaller one. I certainly hope they offer this soon to help defray the cost.
Finally, I have dealt with customer service a couple times and they are friendly and helpful. They seem to be really excited about their product, which is important.
For these reasons, I am updating my rating to 5 stars.
Update 10 months later:
I now use the TENS and EMS modes equally. No complaints at all. I have had to replace the electrode pads much less frequently than I originally thought I would. Also, my original con about the snap problem only happened that one time and I never saw the issue on any other pads.

I use it occasionally after a work out. Seems to help relieve some muscle tension.

Fantastic to be free of cords & outlets. This is the difference between your cell phone and an old landline with a rotary dial. Big improvement over "cordless" models that still use wires to power the electrodes.