One would think so, but look at Glocks knives for example. absolute rubbish. I am guessing H&K just see airsoft as toys (fair enough), just want the money and couldn't care less about who puts their mark on their airsoft. I much doubt they helped design the airsoft version, firstly they are busy producing weapons, secondly because Umarex is not the manufacturer (unless I am much mistaken)
I agree about lemons, G&G has them as well, but that is really not what I am pointing out.
As for your gun, it clearly is decent if it been running for two years. but I still wouldn't recommend getting it before finding out who the manufacturer is. The only Umarex I personally know about is the 417, which is manufactured by VFC, so I am guessing it is darn good.