Although I do agree with League to a point, there are times when quality of hopup chambers does affect performance. I used to have a TSD metal hopup unit in my G36 when I got it. It sucked. Period. The cylinder that the bucking went in was so wide that I had to wrap the bucking about 6x in Teflon tape to get it snug. Even then, a little bit of air was escaping around the bucking. That would affect compression and thus shot consistency. Also, the arm that pushes down on the nub had a lot of horizontal play to it so that the nub was able to rotate slightly. That also threw off consistency. I finally decided to put in an old Echo 1 plastic unit I had and the consistency greatly increased because the cylinder was tighter and there was very little horizontal variance in the hopup arm.
Basically, unless the hopup unit has really bad build quality or if it doesn't stay tuned, then you shouldn't have to worry about it.