In reply to odox: I've used my friend's a few times, so just some preliminary thoughts. The basic screw works very well (just a Helix I think, which are very nice screws). The extender thingy is OK - advantages and disadvantages.
+ve
- you can clip it before fully in if very scared, although not sure how much a protection a half in screw gives
- you need few quickdraws - if you had a rack of speedies this might be a real thing, but I suspect most people will have a mix of screws and therefore are likely to carry the same number of QDs as before.
- you can leave the screw clipped to the rope whilst you take it out BUT this only works if the rope isn't too tight and pulling the insitu QD outwards (cleaning a screw on steep ice for example).
-ve
-how do you rack them? Clip the krab and they hand down low, catch your trousers and you have to juggle them to get the screw itself in your hand. Helixes rack badly anyways and these QDs just make extra tangle
-heavier
-more expensive.