I'm only 5' tall, and when I used one, it was completely awkward and hurt my knees because the motion was totally unnatural for my stature.
The stride was huge for my little legs.
That was several years ago, and I don't know what advancements have been made since then.
My advice, find a good store and try 'em all before thinking about buying one.
We just got a treadmill in January and looked like geeks in the store trying them all, but we're really happy with the one we got, and are OK with the $1700.00 we spent.
Hope that helps,