From the docs:

The Standard Debian Kernel (selectable) can be used for ZFS. However, since ZFS kernel modules are not installed in the Debian kernel by default, they must be built by the ZFS plugin when it is installed. While this process works, building the modules is a long process that requires continuous access to online repos. Accordingly, the potential for a build error exists. For this reason, while the Standard Kernel is very usable for ZFS, it is not ideal.