Anyone used the Kensington Expert Mouse?

Never used a trackball before, but I've heard from a few people that the Kensington Expert Mouse (Amazon.co.uk linky) is very good, and once you get used to it, much better than a mouse, just wandering if any of you guys has experience of it. I would try it out if it were cheap, but it's quite pricey I suppose I could buy one and send it back if I don't like it as most places don't make a fuss if you don't like it and return it after a few days.

EDIT: Just realised this probably wasn't the best area to post this in : / I blame the time