It works reliably.

LLVM is engineered to be usable as a backend for type-safe/memory-safe languages. And those flags are engineered to work right for implementing the semantics of those languages, provided that you also do the work to avoid other LLVM pitfalls (and FilPizlonator does that work by inserting aggressive checks).

Of course there could be a bug though. I just haven't encountered this particular kind of bug, and I've tested a lot of software (see https://fil-c.org/programs_that_work)