I have only just started playing Outcasts in a grow league, and picked up Big Jake as part of the lot to full around with. I have found him a great asset at 5 stones.
His "I Got This" (or similarly named) ability where he counts as 2 models for Strategy VP purposes is great and worth the stone cost alone. In several games, he has been the difference in scoring points because of that.
"Consult the Ancestors" is useful for one or two turns (depending on his health) as a last move during his activation to prepare yourself for you opponents next move. He is not tanky, nor is his tomahawk attack (melee or ranged) particularly special (although the melee trigger is useful to getting him out of engagement, which is beneficial for his VP ability). However, he is not designed to be a heavy hitter or a meat wall. He is a strat/scheme runner, and with his abilities and 0 action, I find him easily worth the 5 stones. For what he brings, I could see him worth the 6 stones he cost as an out of faction mercenary, depending on the strategy (such as interference).