I don’t know the entire science behind it, but they definitely keep the chain much tighter even going through travel. Bit odd when fitted as it all seems too tight and I worry that the chain is too short. Riding it all seems perfect though.
I’ve gone for a guide with a pulley cage however and all is rock solid. Pick up is great. Feels like my hard tail or I guess even a single speed. Foot on pedal, off instantly with power. Got no clain slap, no mech rattle, no chain drop whatsoever. Finally! That’s with 1×10 and a short clutch mech plus e.13 TRS+ Single device. On my old 2×10 (X0) I had loads of problems with chain drop, even with a 2x chain device, but that had a slack mech (older X0 mech).
I could probably do without the pulley cage, but seems fine at the moment. You will *definitely* need a top guide though.