Cheers guys, all good info.
Gave it a go yesterday afternoon, did my general warm up and then something progressively more specific, with some full body thrown in. A few easy deadlifts and some muscle snatches, then normal pullups, then the variations you mentioned.
I was feeling very good, but when I went for the one armers both my elbows started aching quite bad especially in the negative phase and I immediately stopped.
My shoulders were making horrible creaky sounds also.
I'll stick to normal pullups but will go for max speed instead, and will keep working with straigh arms like with front levers and ab-rolls. I found that straight arm worl does magic for pulling power.
Fortunately the elbows problems that I clearly have do not affect my climbing, so I think I'd better sack the one armers and enjoy this period of form on the rock!
Anyway, many thanks for the advices, keep them coming, I'll surely keep checking the thread.