I heard of them. The basic concept is pressurizing the bladder with a bulb pump so you don't have to suck. I never was much troubled by the amount of suction it took to drink from my various hydration systems I use on the MTB or hiking so feel it'd be an unnecessary complication for me. Some of the cons are price, the pump has to work, the bladder is inflated big and stiff, it has to seal very well so as to not lose pressure, ...