I don't associate with the author that well here because I'm not hyped about 'arena allocators' and I don't really care that free doesn't receive a size. I think the interface was okay.

Also 'arena allocators' (this meant something different like 20 years ago so I think the name just got rebranded) are not that good, they make some things easier and improve performance sometimes, they also are liable to use more memory and cause more fragmentation if not used with care. That is one of the many reasons why we slowly evolved away from the old linear allocators, but also because we just wanted a simple and flexible interface to hide complexity.