I can pick on Metro’s specific implementation but I have mostly positive feelings about this.
The pattern I’ve built up in unrelated projects I’ve been on is to reduce the amount of gendered language in general and removing the need to store any kind of gender information to the point where it doesn’t need to be on the signup form at all. From there, using genderless pronouns and preferred names (as opposed to maybe the name that would appear on a passport) wherever possible.
Would love to know what requirements could be imposed on Monzo that might hinder moves towards something like that as they begin to offer current accounts.