I have an F6 and like it, but I have to say that if the only reason to choose it is the back light, you might be disappointed. I tried using the light the other morning when I was running before dawn, and I couldn't read the watch. Of course that may have something to do with my almost-52-year-old eyes, but I didn't find it bright enough.

I haven't had any trouble with the chest strap and find it comfortable enough.