Not really Yamaha specific...but, these tires are specifically on my bike.
I wasn't really excited after riding on this set of tires. I can't specifically explain why other than they didn't do anything that stood out in my mind as excellent. Like, excellent hookup in the loose dirt, or excellent push in loose sand.
The front tire, however, I've noticed that it's like a pizza cutter wheel. Especially in sand. I have to ease the front into a turn because if I turn too quickly (which isn't quick at all), the front digs in and CARVES a turn over hard.
I have a Pirelli mid-hard on my XT350. After eyeballing the two tires--they are both 80/100/21's, I started to think the Michelin was skinnier. Calipers confirmed the Pirelli is a full 3/8 inch wider measured not on the knobs, but on the smooth portion of the carcass.
So, I'm going back to Pirelli.
Once I wear out the back tire, I'm going to throw a Kenda Trackmaster II on it. These aren't the longest lasting tire, but they hook up good, and push loose sand well enough.