The MT-21's rock they're pretty much the best offroad tire which also works on tarmac.
If only sand the MT-410 this is a new specialized sand/mud tire.
You need lot's of deep knobbies for sand and mud, the MT-410 replaced the old MT-44 as the Sand/Mud tire. Only for offroad though, if you intend to use them on the road, MT-21 is the answer.
Good alternative is Dunlop D-606, it's Dunlop's most aggressive tire which can be used on the road.
Read a lot of positive feedback on D-606 rear with MT-21 front combination.