Careful. "Long cage" does not equate to being able to handle larger cogs. It has to do only with the amount of chain slack the RD can handle. Note that Al1943 said, "A 14-34 freewheel would require a long cage mountain bike rear derailleur." Key is the bolded phrase. The parallelogram geometry of MTB RDs is such that the shifting arc is steeper than for road RDs. This is what makes them able to handle the big 34T cogs.
A mountour is a mountain RD. In fact, it's the very first one. Many of the old suntour long cage derailleurs can handle silly large cogs. The VX GT can do 34, easily,