I bought a full set of M12XC tires for my WR450 in preparation for the 24 hours of Starvation Ridge race. Went with the M since the track would either be hard or extremely soft and muddy depending on the weather on the day. It ended up being really goopy clay mud. The tire hooked up exceedingly well, even able to loft the front tire when the traction should have been horrible. Not as great for cornering, but again, I was riding on grease. No signs of any wear yet, but there wasn't any friction on the tire. Early on, some sections of the course were grasstrack, and the tire hooked up great there too.
Downgraded on ease of installation since it's a tire. It's never all that easy, and won't ever be. Didn't rate highly on durability because I can't say for sure yet, all the miles I've put on it so far were low friction.