OK ... the part I'm missing is, if a pump with a Y on the outlet worked as well as the T3, wouldn't that be something people would have been recommending for years - instead of always warning against parallel loops (for the most part)? I never got the impression skinnee was hiding from comparisons with a pump with a Y on the outlet - just that he has already invested 3 weeks testing this as is, and has other work to get to first.

From the simple way I look at it, the T3 is a nice bay reservoir. It has a nifty place to put the D5 pump. You have the option to run parallel loops (or not). For most configurations, it will be easy to fill and bleed ( I say most, cause I'm not to sure I'd be happy trying to use it without top fillports in my Mountain Mods cube). The data provided by skinnee shows that you get nice flowrates with it as well. BoxGods has explained that it does have some differences to a regular top/reservoir system - the main one I see is the amount of space for water at the inlet. This seems to increase the performance of the pump. I dunno, maybe I'm just not understanding the concerns.