I'd been using a 15-key streamdeck for a while (even before KM9. When I got it I wrote a plugin to run inline applescripts on it, which I mostly use to trigger KM macros: https://github.com/mushoo/streamdeck-applescript ). I just got the XL a week or two ago, and I love it. I'm still generally using my applescript plugin instead of the official KM plugin, just because I find it a lot easier to set up - finish my KM macro, copy the applescript it generates, paste it into the streamdeck button, done. I'll probably use the official KM plugin for some of my more involved plugins that take a long time, just as a way to provide some feedback while it's running.
But I love the XL - so many buttons per page! On the 15key I had about 4-5 pages of buttons just for my one main program, now I can fit all my most used onto one screen!