Each user interface has its advantages, disadvantages, likes and dislikes.
Napp-it follows a very conservative idea like a classical desktop application combined with a listing of properties that can be modified. This is what I prefer as I work with it all day on many appliances. Napp-it is basically a tool to manage my storage installations.
If you install napp-it on ESXi and OmniOS is your OS of choice, setup is ultrafast as it means only an import of a template. Otherwise or on a barebone setup you have the freedom to choose among some operating systems like Oracle Solaris, OmniOS or OpenIndiana, install them and add napp-it on top. This cannot be as easy as when you install a system where OS and management interface is tight together and you can install both in one step.
Solaris and ZFS were originally an offer for large enterprises. Luckily Sun decided to OpenSource ZFS so others like BSD or now Linux were able to adopt. Sadly Sun did not care about home or Soho environments. This is why BSD/Linux/ZFS solutions are now so widely used. For years Solaris was far ahead of them and even now ZFS integration is best.
One reason why there is only the commercial RSF-1 clustering from high-availability around, beside some unsupported solutions around Opensource Pacemaker. I work on a simple cluster solution based on iSCSI and network mirror but especially on Illumos based systems there are some problems left regarding timeout/hanging of the initiator on a network disconnect. Hope that this will be improved in Illumos.
Setup for OSX is identical like for other SMB clients. Netatalk/AFP is available but a constant source of pain but this is not Solaris specific. You only need to care about a different, mostly more Windows alike behaviour compared to SAMBA solutions.