I just evolved my Bergmite. It has a slightly shallow movepool, but it has good attack and its defense is pure crazy. I believe it can get over 500 defense with the right nature. Mine has a def+ nature, and i EV trained it, so now it has over 180 Def. at level 37. If you can get the right TMs, i'd say its worth it.
I used one too. It is like the exact opposite of Cryogonal, actually.
Cryogonal has pretty good Sp. Attack, Sp. Defense, and Speed, but poor HP, Attack, and Defense Avalugg Has pretty good Attack, Defense, and HP, but poor Speed, and Special stats.
But Avalugg has monster attack though. To the extent that it made fairly good use until I got to around the E4 with Rock Smash. Rock Smash. However, do not keep it in on anything that even may use a special attack, because it won't be able to take it.
It learns Crunch via level up too, so even without the best TMs, you have a half decent moveset with Crunch, Avalanche, Strength, and so on.