The only guarantee TOFU gives, is "this is the same key as you were communicating with last time" - which is simple enough that people can reason about it, and yet strong enough that it significantly boosts security.
TOFU is an excellent baseline, people who need more can augment it by verifying keys out of band, pinning keys, etc.
Simplicity matters! For code and UX.
Bad UX = mistakes = insecurity.