The +P+ be hype!
As far as if it is safe for a pistol to fire the ammo (regardless of whichever pistol you are using) I don't believe that any reputable ammo company would put out ammo that couldn't be fired in current production pistols.
I know over on Glocktalk.com there was a little discussion about this and someone actually called GA. The girl who answered the phone stated that it is not recommended because of the acclerated wear on the pistol. Perhaps they are concerned about the chamber support also.
I recall that someone on GT used the +P+ and was getting like 1225fps or 1250fps, which is not all that much better then what we (as handloaders) could do with our own home cooking. If you want 10mm power, get a G29 and you'll have more velocity, in a stronger case and most likely a pistol that will be easier to control (figuring that a 10mm pistol will have a heavier slide and stronger springs).
As far as GA ammo, I have their 155gr 10mm ammo and it has shown one NASTY problem. It doesn't hold its seat. When being chambered in my ParaOrdnance P16 converted to 10mm, with a 26lb recoil spring, the bullets are jammed quite deep into the case. With a 24lb spring about 2 trips up the Para/Clark ramp and the particular bullet is turtling into the case. I might drop down to a 22lb spring to lessen the battering the rounds take up the feed ramp, hopefully to avoid dangerous pressure gains caused by this habit!
BTW this is the only 10mm pistol that causes this problem with GA ammo and GA ammo is the only ammo that do this in the ParaOrdnance P16 converted to 10mm.
Derek