I've been using my SafeTurn for 3 weeks now. In that time I've had a moderate amount of night riding.
I wouldn't both using it during the day. It's just not bright enough.
After a bit of wrangling, I have found a place to clip it to my glove. This is much more comfortable than the included strap. The clip is slightly too small, and not quite strong enough though - I have to be careful it doesn't vibrate loose. Thankfully the light is fairly sturdy. I've dropped it twice from shoulder height with no apparent damage.
Exactly where you mount it will depend on your handlebar position, and on how you indicate. I put mine near the centre of the back of my hand. Interestingly, a friend with drop bars puts hers in almost the same position, despite her hand being at a very different angle on the bike.
I still find I have to concentrate on rotating my hand enough when I indicate so that the switch activates. This rotation isn't so much as to be uncomfortable. If the light is upside down the switch will always activate. This is not a useful position, just an added limitation on the possible mount points.
Related to this, it probably wouldn't be possible to use two on the same hand (one for the front, one for the back). This is annoying, since the two cars which have nearly hit me since I got the SafeTurn were both in front of me (and hence couldn't see the light).
I'm not going to bother getting a second light for my left hand. I can't come up with many circumstances in which a car behind me desperately needs to know I'm turning left.
All in all, I'm starting to wonder whether yellow reflective strips (such as those I mentioned in
a previous comment) aren't a better move. I'm still considering using both.