In reply to Tigger:
Were you thinking handled ascenders for hundreds of metres of jumaring up fixed lines, or more a little device to get you out of "oh dear wrong sea cliff"?
In terms of handled ascenders, the petzl gear is pretty light and flows well over thick, wet, mud caked ropes; though technique and practice makes more of a difference. However I'd never clip my jumars to the back of my harness.
If you're thinking along the lines of tibloc, kong duck, microtraxion etc, then it's worth thinking the specific scenarios you'd use them for and that usually helps you decide (using the microtraxion for hauling may screw up your dynamic ropes, but if it's hauling your mate out a crevasse then worth it).
Post edited at 16:52