It doesn't make it any safer because the cast is unchecked. It could be argued it's discouraged[1] for a reason that doesn't really apply to modern C versions where implicit-int isn't allowed anymore.

But while the cast is a matter of style (or C++ compatibility), sizeof(*ret) is definitely superior to sizeof(thing_t). The reason is that people sometimes change the type of ret but forget the change the size of the allocation, especially if ret is assigned to on a different line it's declared.

[1]: https://c-faq.com/malloc/mallocnocast.html