Hey Jason,
One of the important items in my test was to see how much Crud went back into the water when pulling the cleaner out. Here are my results of the top 3
pentair 820/830 dolphin endeavor - all work the same. cartridge on bottom with a mechanical flap. it works decently, but not 100% perfect. some of the dirty water still comes out if you take it out normally..but not terrible. if you flip it over, there is no problem. But the 820 was hard to flip over because of the lack of handle.
Smartpool scrubber - had a flap that opened on the front that allowed the water to escape, but still let a little bit of dirt out if you didn't flip it.
dolphin m4. when I saw how this was designed, I was very skeptical. it is a cloth bag over the dirt inlet flap rather than a spring loaded door. The top of the back has a weight that makes it fold over when the cleaner isn't on. (sort of like those old change purses your grandmother used to carry...when you pushed them, they open.) When I saw this, I knew it wouldn't work. but...shockingly..it was the best. it lest the water flow through the fabric but not the dirt. This was the best performer of all of them. I've only tested it about 5 cycles, but so far, i haven't had any dirt blow back.