Back pain sufferers alert. I am 71 years old with a history of lower back pain. I also suffer from sciatic episodes. I had a cheap tens unit that did very little. This unit is amazing. Its plug and play. As soon as you turn it on you will feel relief. The modes are very different and each one is great. I did a quick review of the modes, but the first one felt so good I have been stuck on it. This is the unit I would give to a friend. Young and old will enjoy it. And, they will remember that you gave it to them. It is rechargeable, so no expensive batteries to continuously purchase. The same charger that your android phone uses. Easy instructions, printed large enough to read, and in English. I just got this unit but so far I do not see a down side. Get this now.