I had heard of these before but they used to be called something else... Can't remember.
I reckon it'd take a bit of getting used to, in terms of 'placement' etc. Plus you'd want to keep some wipes handy for splashes and be able to rinse it after each use.
Personally I haven't a drama with squatting behind a bush while camping. On longer trips I got pretty darn efficient at it, especially on the occasions when I was preggers and peeing every 5 minutes. I wouldn't bother buying one myself.
I don't boat/fish though - I'd be too busy throwing my guts up to even think about how I'm going to pee
So why the hell not?
In a couple of words... Go, Girl.