Can't say anything good or bad about the SR22. I do own a 22/45 RP target pistol and I believe that it will outlast me. As far as I'm concerned the MK series Ruger is one of the top of the line 22's.
+1 to this, and I'll add that the SR22 is super easy to field strip and clean, while the 22/45 is a PITA to put back together until you get used to it.Apples and oranges!
Depends on what he wants to do with it. 22/45 will be a better target pistol, but not very conveinient to carry. The SR22 is much more compact, and accurate enough, but not on the same level as the 22/45 or any of the Mark III's.
My opinion anyway.