Well, the first question is:

What's your pool configuration (including where you are)?

The second question is:

What are you looking for it to do for you?

Otherwise, it's an open-ended question. Lots of people here have them--most love them. Lots of people don't and would like to have them. Many don't and don't see the need.

If your question is: Are they a legitimate pool sanitizing system or a phony, the answer is they are legitimate.