Haven't used them. Considered them when we got the first camper because they were cheaper.
I'm sure they work, but I've found its pretty easy to bend the top lip and top of bed rail on newer trucks. Just the J bolts that attach tool boxes bend the top bed rail. I anticipated damage to the bed with these and went with frame mounts. Also appeared to not allow a long enough connection to get any sort of spring loaded connection in the turnbuckle/chain assembly.
Older truck and/or small camper, maybe, IMO. New truck with fragile thin sheetmetal and a big camper, not so much.
JMO.
Similar with Happijacs. I'd consider the front Happijac mounts to be secure and would use them based on how they distribute the load, but I'd never use the bumper buttons if I wanted to keep my bumper straight. The old 86 Chevy we just bought has one side of the bumper tweaked from HJ mounts and it's a real bumper. Newer bumpers are tin cans comparatively.
TL, while expensive also offer the best angle/location for mounting. The bed and bumper mounts require much larger angles between the camper and the tiedown, which structurally puts more/different stresses on the camper brackets AND is continually "pulling" on the truck bed vs the frame.
I think in this case, you truly get what you pay for.
2016 Ram 2500, MotorOps.ca EFIlive tuned, 5” turbo back, 6" lift on 37s
2017 Heartland Torque T29 - Sold.
Couple of Arctic Fox TCs - Sold