So who runs one and what do you think?

I am mainly confused on their 2 models. They have one that is progressive and one that is non-progressive.

Does progressive mean both pump are on full time and ramps up when required?

And non-progressive mean the secondary pump only comes on at a certain pressure trigger point? So its either full on or full off?

I plan to run E85 with this so which would be better and why?