Part of my armory I have an H&K mp5 .22lr, I was told the GSGs are knock offs and have since been sued by H&K. I noticed at shops and shows there are a lot more GSG parts (mags, rails, high cap drums, etc) that are offered with H&K.
They are nice rifles and look better on the wall than anything else. I hate taking my .22 to the range when everyone else is blastin ARs and AKs , so it's stays on the wall until I need to shoot rabbits or need to teach anyone the fundamentals.
Let us know how it performs!