In reply to dannorris: In the past I have - I think I've had both yetis and extremities on Asolo extremes (I think it might be them in this pic: http://www.ukclimbing.com/images/dbpage.php?id=22939 although I can't remember). As I remember they used to pop off with annoying regularity. They helped a bit but not too much. I became convinced that my Asolos used to suck moisture in through the welt which isn't covered by a yeti gaiter.
It might be unhelpful advice, but have you considered saving the fifty quid for a pair of gaiters and putting it towards some plastic boots? I haven't regretted doing that! Also I use some ski gaiters from Decathlon with the plastic boots and they cost I think four quid. Even if you are just touring some say T3s are the way to go.
In reply to TobyA: For years I used yeti gaiters with my leather XC boots (can't remember the model but fairly stiff for a leather boot, similar to your extremes) & had few problems with them comming off. At the time most of the guys I skied with did the same (I was Aberdeen based mostly at the time).
And much as I like leather XC boots for gentle touring, plastics do have many advantages
