I recently installed the 2nd generation 25L bags from MM. I like them pretty good.
I just couldn't pull the trigger on the most expensive soft bags extant (the 35L bags). They look a little too bulky for me, & I really don't need that much space, myself.
I will say that it took hours to find the correct mounting points on my Rumbux rear racks, due to their design (not square). But now that their on good, no need to ever take off, I reckon.
I'd also say that there several things about the MM bags I don't like, the main thing is "let's make everything a backpack!" mentality. I also got a 30L duffle (its a backpack also!) that I don't like 1 bit. Talk about overly complicated & bulky design. I tried it for an hour with different gear, positions, set-ups, all for naught. I'll likely sell it soon.
So i got 3 backpacks, I mean bags.
If MM is listening, I don't need bulky backpacks that are also bags. I just want good bags. I don't need backpacks, at all. I strap bags onto my bike, not my back, & carry them. Lotsa good space is wasted on interior backpack straps, that could otherwise make a more streamlined, less bulky bag.
MM also needs to come out with a true rear rack bag, along the lines of Moose Racing. I'd like to see a smaller bag that specifically fits just a rear rack, & also a larger bag that fits a rear rack / pillion plate. & it certainly doesn't need to be a dang backpack either.