In reply to Robert Durran:
I use the Alpine Up, which is the Click Up for half ropes. (Nothing better for half ropes, in my opinion). I have a lot of experience with it and I'd say short-roping is simply not an issue; even if the device is locked up, which almost never happens when you know how to handle it, it is very fast to release (again, if you know how).
I think that one reason some people lock up the device is that the belay with it in the standard palm-down belaying position used with ATC-type devices. For half-rope handling, I much prefer having my brake hand palm-up, and this position has the additional benefit of making accidental locking even rarer and releasing even easier. With an ATC, the palm-up position has the disadvantage of weakening the climber's grip on the brake strand, but with the assisted locking of the UP, this is not an issue.
The drawback is that the belayer does have to drop their brake hand below the device to initiate a catch, and therein lies a trap for the inattentive. This isn't a problem for me personally, because I learned to belay and climb years before inattentiveness stopped being perceived as a fatal failing and began to be viewed as something nearly inevitable that required a technological solution.
Post edited at 14:21