Personally, I think it’s a good move. I get the desire to avoid hiring “suits” and perceived industry veterans as they might not have the same ethos but I think that’s probably not a huge risk.
Sartorial choices aside, Monzo wouldn’t have sought out someone they didn’t think would buy into their approach. Likewise, I doubt that someone with entrenched industry views would accept the job.
I think having someone who is perceived by the industry as a serious heavyweight can only benefit Monzo. It adds to their credibility and they’ll have someone who’s been through some of the challenges they’re going to face in the future.