I own 2 GSG-5's and they shoot great. If your son go's with the GSG-5 he will need to install the screw kit to keep the bolt from braking. Check out http://www.rrages.com/
After I installed the screw and pin kit and installed a red dot sight I have not had any problems with the gun, the disassembly for cleaning is easier. When the bolt is removed there is a spring for the bolt hold open that is exposed and you want to make sure you remove it when cleaning, or it will fall out and then re install it before putting the bolt assembly back in. I shoot old cd's at the pit and with the red dot I just keep shooting the pieces until you can't see then any more. There is a ton of stuff for the GSG-5, stocks, forearms, mounts, 110 round drum mags, ect. I like the looks of the SIG and will get one some day but right now I have thined the heard of semi .22's down to the GSG-5, GSG-5P, and my marlin papoose. I hope this was a help and if you have any questions on the GSG-5 I would be glad to answer then if I can.