I have a g36c, and have had no problems with it so far. Main reason I purchased it was for the quick change spring, so I can go indoor and outdoor with the same gun. It also had good reviews. I hope other companies use it on their products soon. Parts are hard to find. They do have a facebook page, and that's where I got an email address for customer service. I ordered a ball bearing spring guide from them, haven't got it yet, but it's only been 5 days.
I would have gotten the G36K, but I didn't want to pay extra for the scope/carry handle that I was going to remove anyways, since people say the eye relief was bad, and it had no way to mount rails on the front, which meant more money to purchase another handguard. They should sell the scope/carry handle as an upgrade accessory.