I have one that I've been testing for many thousands of miles (ask CJDesigns if interested).
I'm super happy with it. Yes it back flushes whatever is in the fuel... Back in the tank but my fuel filters look like new (lightly stained). I am not worrying about clogging my filters in the middle of nowhere and it's paid for itself already.
Any questions, I'm happy to give my 2 cents.
Update: here is the one I have http://www.cjdesignsllc.com/efi-purge-modules/