In reply to Neil Williams:
> (In reply to origamib)
>
> Personally I'd rather anyone belaying me used a device they were familiar with and used normally, not a completely different one I lent them and they'd never used before.
>
> Neil
The Click-Up and Alpine Up work exactly the same way as a tube-style device for both taking in and paying out, so there is really no problem with unfamiliarity there. Lowering is trickier because you can release too much friction, a problem shared by the Grigri, which is, however, worse in this regard. The important new thing to learn (and it is easy) is how to quickly unlock the device if you accidentally lock it while paying out slack for clipping.
The Smart and the two Edelrid Juls work the same as a tube-style device for taking in but in general require the brake hand to also lever the device away from the belayer's body in order to pump slack to the leader for clipping. This makes them inferior to the Alpine Up for half-rope handling, but they are cheaper and lighter and the Jul is a lot less bulky.
I regularly give an Alpine Up to belayers who are experienced with tubes but have never used the device, and after a minute or two spent showing them how to rapidly reverse accidental locking, have never had any issues with the belay. But this is not the same as handing the device, any device, to an inexperienced belayer, who might invent all kinds of ways to screw things up.
None of these assisted lockers can or should be trusted to catch falls automatically. What they do is add extra braking power, and so make it less likely that a belayer will lose control for some reason.