I’ve owned a Procaliber SL, which I’m thinking of selling, for a couple of years and find it rides really well and is comfortable for longer rides. Don’t expect to feel a massive difference as the system is designed more to take the buzz out of the trail rather than absorbing obstacles so you have to treat it like a hardtail. You do get less of the bum bounce which you typically associate with riding a hardtail. You don’t feel it robs you of any effort when laying down the power.
Not ridden the BMC so I can’t comment how active the rear end is over obstacles and when pedalling but it seems an interesting option although if I were to go down that route I’d rather go FS with a Trek Top Fuel.