I have one. I bought it way back before we officially started TTC.
I don't use it much anymore, because I know when I'm O'ing now... But it's great. I could always see the progression of ferns and they lined up with my OPK's and temps... so I'd say it definitely works.
The only problem with mine is that my little light in the bottom burned out. I don't know if there's a battery to be replaced or if it's one and done. But, I've got a tiny flashlight I use and the lens is really the most important part.