I have the mountain derailleur on the back of my bike with a compact (11-34). It's a Deore XT with an Ultegra front derailleur. It's a lot of low gears, although the range in the middle of the cogs feels widely spaced compared to my triple with an 11-28. However, i am now used to the feel and it's fine. The combo works perfectly and I ride up steep grades (10-18%) on a regular basis.