I've also got the early non-adjustable power version. Had it from new; 30 shots per charge, and after 5 years ownership, it still chronos at 35ft.lb with Bisley magnums, which seem to suit it best. Heavy to carry around (even with a sling), and definitely helpful to use sticks/bipod. Zeroed at 40yds, and does the biz on rabbits with ease. It gets an awful lot of use on my permissions, and has been 100% reliable throughout. No intention to sell at the moment (what would I replace it with that would do the job any better?)
I have found that if I take the gun for an extended zeroing session, on the 3rd fill (pellets 61-90) the POA changes by a noticeable degree. For example, using the laser/scope for rangefinding, I found that a shot at a target requiring 1 mil-dot hold over would only need half-a-dot hold over or even slightly less. A shot at the zero range requires half a mil-dot of hold-under. I can only assume its something to do with the gun getting hot through extended use (how often do you shoot 60-90 pellets in fairly quick succession in the hunting field?), and the air reservoir on the rifle certainly is much warmer to the touch than when I start the session.
I avoid the 'problem' by never taking the air cylinder to the permissions, so a max 30 shots per visit is my limit.