I think Keith and Dufftown see themselves as more of a community asset than a preservation movement. I gather the route is dulled by speed restrictions so can feel like a bit of a crawl.
I will go on it some day though!
I'd recommend it - it's the only preserved line I've been on where staff hand out whisky and give a running commentary on what you can see through the window. I appreciate that probably won't happen every journey, of course, although the scenery would be pretty good all year.
It also goes from somewhere to somewhere else, unlike a lot of preserved railways which just end in the middle of nowhere. You do need to be a DMU fan, however.