I've played against them. Daemons vs. Nippon. It was a very interesting game and fun game. Toward the end of the game it was a race between my instability checks and the break point of the Samurai. Ultimately, the Daemons won due to some spectacularly good die rolling.
The Samurai have a break point like Brettonians, which means they can waste lots of peasant units if they want to. With the Divine Ancestry and Retinue options, the army can be very anti-magic and can have some interesting special abilities. The Mystic makes a great retinue option, as he effectively provides a second command die roll.
I highly recommend giving the army a try.