Every so often, the latest version of ZPE is updated. But even more commonly the early release version of ZPE is updated.
It is essential to know that when using early release versions, which are available parallel to the stable releases, ZPE early releases are not stable. This means that they could feature bugs, performance issues, features not intended for a final version or even features removed from them entirely. In general, early release versions of ZPE are not considered stable.
So then, why would you download it? Early release versions allow you to download a pre-release version that allows you to detect bugs before the release of the final version.
Why you shouldn't use it
I'd recommend against this version unless you are really keen to find bugs. This version can harm your system or might break existing programs. It might also be incompatible with precompiled code.