Hi Andy...

I use then occasionally in the gym, they are a good workout, and a reasonable fellrunner would get about 4000ft in an hour out of them at a steady pace.

Although i have to say that personally i think using a treadmill at max gradient (15% preferably) is more specific and more benefit.

Certainly if you're looking to purchase one then i'd opt for a treadmill over a stairmaster... a really decent treadmill can be had for around £1500 (many cheaper options available), but a stairmaster costs thousands.