Been using the Arbiter as both one of my 'Mechs and OpFor when playing against the bot in MM in prep for my Quasit MotW. And, yeah, wow.
Armor isn't awful for its size, but not inspiring, either. The heat from its heavy rifle is nearly crippling against any serious opposition: three shots in a row, and you're in trouble. And, of course, being an IndustrialMech means any critical hits become vicious fast, are far easier to get, and quick to cripple you in physical combat.