They're not meaningfully different from the perspective of the programmer. You call a malloc-like function and get some memory back. The total dynamic memory use of the application is simply capped. You can do this even with libc malloc in a standards compliant way (e.g. Broadcom used to ship a malloc implemented as a series of pool allocators over statically initialized arenas), it's just uncommon.

If you're the programmer who has to provably meet hard real time constraints, the difference matters quite a bit.

> You can do this even with libc malloc in a standards compliant way

This is what I do in nontrivial embedded projects. It makes things easier and less error-prone to replace malloc()/free()/etc implementations directly with ones that behave as needed. And then you don't have the standard implementations sitting around waiting for a new dev to accidentally use them.