I have a GSG-5 carbine. It's been a fun little rifle. The plinking fun is all out of proportion to it's price. Obviously not a battle weapon, but for annihilating cans or paper it's a lot of fun. Mine's been dead reliable with cheap bulk .22.
If I had to do it over however, I'd get the GSG-5K pistol. Then when you SBR it (And you WILL want to) you just need to by a stock. I'll have to cut my barrel and put a threaded adapter on when my Form 1 comes back.