In general you shouldn't expect FORTH to be fast -- it uses the stack far too much and the way it does branching kills branch prediction on modern CPUs.

However it is very small and a lot of fun to write. If you are looking for a system that can run on baremetal and where you can completely understand the system from top to bottom, then that's FORTH for you.

Compared to C, FORTH has an extensible syntax and features like exceptions. Compared to FORTH, C is a lot easier to write significant programs in.