Had it for 2 years and have yet to use it.
I just moved from Phoenix, but in Phoenix, the need is not all that great.
I set up when it was warm, was going to set it up during the winter, but it never got to needing it, so I just didn't do it.
I am setting it up on all my tanks as they go back up after the move. I am not using ANY in tank heaters at all, too much clutter
I have many friends that use them exclusively, and know they love them, I have spent a bunch of time with them and their tanks, so I feel like I have used them and know the value already.