I had an x-25, but retired it quickly. I liked how it splits though, and stepped up to the X-27.
I am tall, and it is short. It's pretty easy for that tool to skate off a log and come straight at your feet or shins, particularly if you are fond of putting a log to be split on top of another log as a splitting base. Truly scary. A slightly missed or poorly delivered strike can do you a nasty injury. I've never had that experience with any other splitting tool.
I'd recommend the X-25 only for shorter people, in which case it is still an excellent tool.
Somewhere on this site there is a thread dedicated to that discussion.