I have been using one for almost three years now, and really like it.
Customer service has been very good (even got an email reply day after christmas).
It is pretty easy to use and I for one... really like being able to check on my beers while I am away... really helps in timing when to allow the temps to free-rise based on gravity.
Overall, I think I just love being able to check on it without opening the fermenter, and also being able to do it while I am checking E-mails on my phone (for the umptheenth time that day)
It is a toy, and not something I would buy as a means to make my beer better, but it has upped the amount of enjoyment I get out of brewing.
I guess the best way to rate it... if my beer bug died today, I would have one in the mail in the next few weeks.