Dave's middle picture looks very much like a setup I bought a camo version of when I was going to be on crutches for about 12 months 3-4 years ago. I couldn't get down on the ground except by falling and then couldn't get back up. Bought it for predator hunting in hopes I could carry it on my back like a pack to get to stands since it came broken down in a nylon bag and was easy to assemble in the field. Turned out to be too heavy for broken ground on crutches, so it still sits unused out in storage. Mine swivels 360 degrees and has an adjustable armrest for shooting rifles, but I can't remember if it has a pistol platform like Dave's has. BTW, I still managed to predator hunt while on crutches with a Safety Seat that broke down into a belt case for easy carry. Is that a dedicated predator hunter or what?
Have also been a serious long range varmint hunter with specialty pistols for decades. I've built a lot of portable shooting benches, have a mechanical BR rifle rest, tried my commercial and home made rests and bags, etc. What I settled on for shooting off a bench is Harris BR swivel bipods. I can shoot long range much more accurately with this setup than any of the others. It's what I used for the 1000 yard matches when I shot them with my specialty pistols. While I have several, my bipods all have the quick release modification so they are very fast to switch between firearms when the shooting gets fast and furious in the digger fields and the barrels get hot.
L.