In reply to iksander:
I use it in click-up mode with trad gear all the time. In fact, I think one of the main reasons to use such things is to guard against the rope slipping through the device. This slippage is supposed to be a safety valve to keep forces lower on protection, but I think it just as likely that, even if the belayer doesn't totally lose control of the belay (and the probability of this goes up as the rope diameter goes down), the extra distance fallen makes it much more likely the leader will have a nasty collision with something.
For most climbing falls, the assisted lock-off doesn't raise anchor loads, because the friction in the system would have kept the rope from slipping through an ATC-style device and so the safety-valve feature would never have engaged.
This leaves a few extremely severe fall situations in which the slippage would happen with an ATC-style device but not with the assisted locker, with the theoretical potential for 20+ kN on the top anchor. Most people never have such a situation in their entire climbing careers, so the question is, how much risk (from the leader falling further, belayer losing control and getting rope burns) do you want to add to more likely climbing situations in order to reduce the loads in very rare situations? I don't think anyone can offer a decisive argument for the choice, it is a matter each climber has to decide for themselves.
I might add that of all the devices, the Alpine Up transitions from assisted locking to friction mode the fastest and easiest. All the other devices have to be unthreaded, reversed, and re-threaded, whereas with the Alpine Up the belay carabiner has to be shifted from a slot to an adjacent hole. The leader is off belay during this transition for sure, since the rope is out of the carabiner during the shift, but it can be done very quickly. This means that if the leader encounters a string of dicey protection points, it is not impractical with the Up---unless the leader is in a really tenuous position---for the belayer to change belaying modes.
Another very occasional advantage of the Up is that the belayer can intentionally lock it up and then let go of the rope to do something else, like tie some gear the leader needs onto a tag line or take a hero shot of the leader, to go from the sublime to the ridiculous. Of course, you can tie off an ATC-style device pretty quickly too, so I wouldn't want to make too much of this feature, but it is quicker to do and release than the standard device tie-off.