Definitely ruthless. Krrsantan joins Dr Aphra’s crew in the comics but as soon as there’s a bounty on her head, he gets fed up of her and begins hunting her down. I think that’s good example of how quickly he can change sides.
He’s also fought against Obi-wan, which is where he got that scar over his eye, but he didn’t do too badly against a Jedi master. A formidable opponent for sure. If Boba fights like he did against those Nightwind soldiers, he’s screwed.