In reply to BruceM:
Thanks everyone. Really useful info.
George: Thanks very much for your reply too. For somebody who, as you say, can't be completely impartial, that's a pretty objective review and really useful info. I wish all manufacturers would talk like that -- the marketing types won't let them!
So it sounds like there are a few subtle differences, but all will do the job. Basically it comes down to "fit" and style.
You see there is another use of these tools that I'm thinking of. I don't climb at walls -- therefore I don't climb all winter -- because walls inherently have shallow crimpy/odd-shaped holds to try to make things harder, rather than the 3D infinite-possibility-hold climbing you can get outdoors. About 15 years ago I knackered my wrists through both climbing and computers and have to be careful how I use my hands. Outdoors climbing can be more varied and "open handed", but walls inevitably have at least one hold per route that is a wrist/tendon "breaker". In winter, ice tools don't "hurt" so I can have a bit of fun there. But I'm a low-grade scaredy climber so get limited practise there. So basically I get no regular climbing action throughout winter, and every April/May have to start out from scratch on real rock. These kinds on tools could do something towards filling that gap.
Which is an exciting possibility!
Another possibility is that these kinds of tools may only work successfully on juggy holds that are OK for my tendons/wrists anyway, so they may not add as much value as I'd hope. But I suspect they might be more useful than that.
I think my first step is to venture back to a wall and have a look and a think about how it all might work.
Cheers
Bruce