The only problem is that the shift is entirely dependent on the strength of the spring. When the spring gets weak with age, the mech stops working or (worse) jumps to a higher gear as you rise out of the saddle.
How do I know this I wonder??? RR mech ownership.
Another supposed innovation by Shimano to bring about planned obsolescence.
In its favour, if you run bar-end shifters with drops, the RR mech means the shifter faces down when in bottom gear (and most likely to be out of the saddle) This stops you banging your knee on the shifter, which is why I fitted it on the first place. But 2000 road miles later the spring weakened and it got tetchy.
As far as I know the springs are the same just connected at different corners, well the springs look the same to me. I've had a RR LX mech from new since 2005 on my RTS and it's still working perfectly to this day?
Ps) I always park my RR mechs in granny ring and middle of the cassette.