I got a set of them a few years ago and I like them a lot. As a matter of fact, I pushed pretty hard when Festool told me they initially decided not to bring them to the U.S. I doubt that I was the cause for them changing their mind, but I would like to think that I had an impact on that decision.
I really like the telescopic ends, which is not that big of a deal, until you realize that the tape gauge also telescopes with it. That is cool. The stops are very nice too, and that is the primary feature I use them for, aside from the extended support. I wish I could explain more, but when I moved my Kapex into a 30 foot permanent cutoff workstation, I put the extensions into storage until I need to use the saw for portable use. As with any of the Festool stuff, it takes quite a while to realize how many little features are hidden in the design, and I know I hadn't gotten around to learning them all before I relocated my saw.