When I first tried the XTt, (recently, it's FAILED on me before) the flow was blocked by some gook that must have slipped into the tubing while it was in the garage, this was prepicture and NO FLOW. So, I opened it up and removed whatever it was, cleaned real well, put it back together and the flow is in the pic
To be fair to the XT, when I first got it I had it in my gamer for awhile and it did live up to the temp reduction as advertised. One day though it got clogged (I think with colorant?) and stopped letting any water through. If you have one of these, try and blow air through either the input or output - you'll pop your eardrums
you can see how much more the restricted XT is compared to the GTZ from the pics. Remember, both blocks connected to a Mag7 700GPH aquarium pump and then run through 50ft of 1/2 OD copper tubing, then through a combined 25 feet of 1/2 vinyl tubing before it gets back to the pump. By no means an easy task for the pump, but....
First pic with XT, second pic with GTZ