I've had one for a year or so. I use it mostly on my black powder match rifles, and on my .308. It doesn't affect the POI for my very heavy barreled rifles, but on my varmint profile .308 it will change POI by nearly a minute at 300 yards. It doesn't seem to affect group size as far as I can see.
To me the biggest thing is that I can use it in all kinds of weather. It's also much more reliable than my Chrony ever was.
Chris.