It’s designed to completely eliminate pedal induced bob. You CAN set it up with sag, but it was designed to be set up so that the shock is right at its full extent just as you sit on it, as you pedal you effectively extend the suspension and it “locks” against the max point, hence behaving like a hard-tail on climbs and under power but “relaxes” back into a 3-3.5″ bouncer when not pedalling.
The earlier shock was not fully strippable and the damping side failed. The newer shock was fully servicable but you have to be quite careful to clean the shock and strip and de-grit it if used in mud a lot as it gets mud under the seals and chews up the shaft (as with any shock). You MUST take care of the pivots or they eat they wear the frame and the rear end (just the seat-stay bit) is 140+vat!, having said that if you get one with good condition pivots and install one of the full ball bearing mod kits you can buy it’ll last forever.
Mines a 2004, I got it in 2007 and it’s been fine for me for that time, managed DH courses in the alps (done at pace, not pootled down) and weighs in at 28lb built in a not particularly light fashion.
I love it. I miss my longer travel on the downs and the suspension can take a little setting up but once it’s right it feels lovely and sprints really well.