I find them to be a fascinating concept, but keep not ordering one because:
1- expensive
2- they go on guns I point-shoot just fine
3- how do you activate it as reliably as other laser options? (as in, the lasergrip concept means I grab the gun, laser is on, no switch-flipping needed ... the rear sight replacement doesn't do that, or does it now?)
4- batteries (am I wrong? does it take a common battery I can stock up on for cheap?
It is appealing in that it doesn't add bulk to a carry gun, and wouldn't interfere with an existing holster