I never had any problems with the deraillieur shift on my Brompton L6 or hub. No more problems than you would get with a deraillieur specced road or mountain bike. Yeah if you ride it for a week in pouring rain then yes the change might get a bit difficult because all lube is washed off the chain making it very noisy and the crud and grime builds up, but what deraillieur system wouldn't suffer the same? Just needs cleaning and re-lubing then all fine again. The IHG is fine.