I usually buy a place only with full-flexi mortgage. That Bangsar semi-d for example was purchased by a full flexi 15 year mortgage. Each month the mandated repayments are RM4329. However every month I would pay in RM580 extra towards the principal amount. (From the rental while my dad took the rest)

On the 10th year, it was 4 payments away from the mortgage being settled in full and was remortgaged.

There isn't a 1 size fit all answer as different banks give different meanings to the term "flexi" and now am finding out there are also differences between how a bank defines "full flexi" as well.
As a whole, most if not all with the term "flexi" in it you can do some advance payments to reduce your loan tenure but some now even on a full flexi will limit the amount of payments you could make.