SMS 75 Is quite nice with the shape of the bladder. Find it keeps me in a better trim then the SMS 100 or my DR nomad Xt. Both the latter's equally good, but definitely heavier. Hollis doesn't really advertise the SMS75 as a multi system, but it does have slots at the back to but the tank band through for back mount. But found backmount on the 75 abit flimsy, maybe cause if the nature of the soft plate/harness. One thing I didn't like on the 75 is the plastic d-rings at the waist. Broke within a few use and swapped it out for conventional d-rings.
Between the SMS 100 or nomad, I prefer the nomad. Find it more adjustable and seem a tat more streamline then the 100z
In hindsight, I would have gone with the SMS50 instead of the nomad, or even the SMS75 if it was out then.