In reply to GridNorth:
I got a free trial of a pair for a day in Kaluymnos. Needless to say it was completely inconclusive. We did quite a long days climbing over on Telendos but didn't push our grades. I wasn't unduly tired at the end and had recovered well by next morning but I had no way of telling if the sleeves had any influence on that one way or another. It was early in the trip and I may well have recovered just as well or better without them.
As for comfort, I thought I wouldn't like wearing them but put them on early and by the time we got to the crag I has=d pretty much forgotten about them so it wasn't a bit issue. BUT more or less the price of a resole for something that may or may not have any benefit?
One suggested mechanism was that by preventing/reducing arm swelling it forced the blood to pass through more quickly so that waste products were flushed out rather than retained. However, to me it seems more likely that if upstream blood pressure is fixed and the blood vessel size is restricted then blood flow would be reduced (if you are doing some plumbing you don't reduce the diameter of the pipes to get a more forceful shower!) so this seems more like a pseudo-convincing reason to buy than a scientific fact.