I am assuming that Fil-C introduces orders of magnitude less overhead than ASAN or Valgrind.

Also, it’s probably fast enough for apps to be deployed in something like a staging environment for integration tests to run against them. Production deploy/release can then happen using a tagged version that gets compiled using vanilla GCC/Clang.

I'm not sure about the speed of ASAN, it may be comparable but doesn't guarantee memory safety. It's only for catching mistakes and not secure against an adversary. Valgrind is dramatically slower.