I have a servo ABS 1150.
ABS is great when you need it (I've missed one idiot who turned right across my path on a cold wet morning, and I felt the ABS cycle so it would probably have been different without it).
ABS can be a drag off road. When I forget to turn it off (not always convenient anyway when just using a couple of kms of gravel road between bits or tarseal), I don't like the "no brakes" effect particularly on rough surfaces on steep downhill approaches to bends. This may be an effect of the "anti-stoppie" algorithm that releases the front brakes when the back locks. Sometimes happens on the road (e.g. downhill, poor road repair that allows the back to lock briefly) but I've got used to it. Brakes are semi-linked (front brings on back, but not the other way round), so hard to avoid.
Servo makes the bakes rather sharp at low speeds, but nice and light the rest of the time (when I switched from a Honda the servo brakes were the same sort of two-finger stopping I was used to, non-servo reminded me of heavy old 1970s Guzzi brembos - worked, but needed a fair pull).
Servo on the back brake releases momentarily as it switches to lower-power mode after a few seconds stationary. If using said brake to hold the bike on a hill you roll a few cm (but it feels closer to a metre the first time it happens).
My servos haven't failed, so no comments from me there.