MFA at my TOC isn't worth the paper it's written on, disciplinary wise. In fact, parts of it still refer to BR.... The triggers are also pointless. A former colleague in my old role got MFA'd because he had two weeks off recovering from an Op.
Your TOC may be different but I was MFA'd in my old role just before I was due to go driving and they told me it wouldn't affect it. It was only MFA1 though and the biggest chunk was because I'd had a week off after a car accident.
Just because something's brought through from BR doesn't mean it's irrelevant though, as far as I am aware anything not covered by DRI or more modern agreements might end up being resolved by the 'blue book'.
There's also the odd tale of guards with awful records for playing the system, going sick especially part way through a job, niggling about rosters, holidays, emergency leave, claiming to be bullied, claiming unfair treatment etc, constant aggro with passengers yet still getting a driver's job despite MFA stage and all of that. Far be it for me to say that the guards managers were more than happy to pass on such individuals - but I know I've seen it happen.
For some people being on an MFA stage when applying for other roles would be more of a hurdle than for others.
I've been MFA'ed for modest time off after a fatality in the past, it's a ridiculous system and has no place in a post-Covid industry as it clearly discourages people from having time off sick when they need to. I know myself in the past (~18 months ago) I've been in work when I should really have been off sick, the only reason I was in work was because of MFA and wanting to keep a clean record.