I have had a F1 Mainframe for 4 or 5 years and personally really liked it. It took some time to get it dialed, ultimately I had the larger padded harness and a K4 belt on it - was bomber for me. The only thing I didn't like was the load shelf hoop thingy - never used it for anything and was always kind of in the way. So I got the new Mod frame when it first came out. For me it certainly is not a "game changer" in any way shape or form. I think they missed out on a few features for individual adjustability - one size hip belt makes no sense to me. I took the K4 belt off my F1 and put it on the Mod frame and definitely fits better and supports the weight better - I think that is purely a sizing issue. I have rucked probably a few hundred miles with it with weights from day pack to about 70#. I think it feels similar under weight to the F1 but IMO more "tippy" - I think being narrower it tends to roll side-side a little more bending, twisting, etc. I have a harder time putting it on with weight for some reason and probably I just need to develop a better technique - might be a by-product of being so narrow as well. I think it's a bit more of a pain to load - my F1 was literally 3 buckles and go most of the time.
I know load lifters was always a big complaint for folks with the F1. I had mine setup so it had good, noticeable function. I'm not that impressed with the load lifter/adjusters on this Mod frame personally. I don't feel like they "rocker" the load as well and are often the only straps I have to adjust repeatedly out rucking - seems like they slip or something else is moving, I dunno.
My wife says the Mod frame just looks small on me (but she says that about other things as well...) - I'm 6'5" - so maybe that has something to do with it and the one-size-fits-all frame.
Anyway - it's OK IMO but I probably would be just as happy with the F1 weighing out the pros and cons.
Day pack setup: a sustainment pouch molle'd on frame containing hydration bladder and extra gatekeeper straps, a large pouch molle'd below that with my kill kit - those two items never leave the frame, a single large batwing with whatever I need for the day, a lid that has nothing, a small pouch on left side hip with gels/salt tabs/lighter/fire starter/headlamp, right side with the "double threat" pouch that I toss garbage, gloves, extra water bottle, whatever in for quick storage:
F1, simple, brainless, strap n go - right up my alley:
