I have the camelbak Palos and it definitely took some getting used to; however, I’ll never go back to a backpack unless absolutely necessary (rare for me).
Loosening during rides was an issue for me in the beginning but then I bought the strap holder deals (sorry can’t remember name) and it stays nice and secure now.
I carry 50oz water in bladder, pump, tube, patch kit, multitool, levers, and a snack. Sooo glad to get those damn straps off my shoulders and the pack off my back. Admittedly, I do have to adjust it slightly (just hiking up the position while riding) several times a ride but, for me, it has become second nature and the benefit outweighs any cons.