He's mostly correct about lots of things, but not about everything (for example, he hated on everything GrapheneOS just because its lead dev is a bit socially awkward). Plus he's overly dramatic and verbose which can be annoying. Sometimes you must be to get abstract or complicated points across better, but I still feel he's too aggressive in that regard. I also like what he's trying to achieve with FUTO in general. Overall, he's a great and valuable activist who has almost all of his eggs in the right baskets.
He said he wasn't going to use GrapheneOS anymore because Daniel Micay threatened to blackmail him because Rossman had made a comment on a video describing his behavior online.