Re: ST-M580 LX STI Dual Control Brake & Shifters - £18 a pai
I like them too. Clearly never took off at all and shelved by Shimano. I've had LX, XT and XTR pairs, currently using a pair of M960 that I got off here for £15, which is an indicator of their popularity...
It might be a coincidence but in terms of lifespan I've never had a problem with the MTB ones, unlike the road STIs which always seem to develop shifting faults sooner or later!