They are worth the investment! I picked up a GSG-5 Gen-2, which is a little different than the GSG-522. GSG (German Sports Guns) came out with their version some years ago. When I snagged mine, it was $150 bucks more than they're going now. I don't know all the details, but HK sued GSG to make cosmetic changes to the gun before they came out with the "HK MP5-22" manufactured by Umarex.
There are some drawbacks! The rifle uses screws for assembly, and they strip easily! You can pick up a replacement screw kit online, and they work a lot better. You can use the parts with the original rifle, but sooner or later, you'll strip one! Especially if you shoot it a bunch! Which I have! I put 1400 rounds through mine, and it pretty much feeds most 22LR. Remington Golden Bullets are not so great, but does well with Winchester Dynamax, CCI Blazer, and of course the CCI MiniMags shoot best!
It has good crisp trigger release, and is pretty accurate! It's not a competition Target rifle, but it gets some tight groups at 50 and 100 yards. The cool factor is something too! It's too much or big a hassle to actually get a real MP5 or 9MM knockoff! So why not a 22LR version with the fake suppressor!
Check out this link for all you'd ever want to know about the GSG-522
Get one and have fun!