I was tossing the idea around of mounting a friction thumbshifter on a
mountainbike with a 9 speed cassette. Has anyone done this and can
they comment on the results? How easy is it to shift into the proper
gear while riding without going too many/too few gears or skipping?
Have you used it racing? Have you tried mounting it upside down on
the bar (perhaps switching the right and the left to retain the same
relative angle/range) to allow for a more natural thumb shift?

Another option would be to mount a bar end shifter on the end of a
flat bar. Has anyone tried this and can comment? I can see some
positives and negatives to this setup. I could use indexing if I
wanted but it might be harder to shift while still keeping a hand on
the brakes/bars. Also trying to navigate through very tight spots
between trees or banging off something/crashing would almost
definitely create shifting problems which would have to be
straightened out before riding again, something that probably wouldn't
have to be worried about with a traditionally mounted thumbshifter.

I know about Paul Component Thumbies but would prefer not to spend
that much money for the shifter/mount combo. Barend shifters mounted
regularly on the flat bar would be half that price and friction
shifters would only be $10 or $15 max.

Thanks.