Haven’t used the FHF folding seat, but did rig a Phoenix Shooting Bags Glassing Pad to my self-made turkey belt using some straps I had. Cinches up nice when walking and can loosen straps quickly when I need to sit or detach all together. Works very nice and is a slick setup overall.
I started with Marsupial and then went the full gamut of bino harnesses (FHF, Sitka, Kuiu). Nothing seemed to work as well as the Marsupial for my needs so I recently went back to Marsupial and sold the rest. I do not see myself trying anything else.