Does FreeNAS give you the ability to run a VPN server so that you can connect to it and have access to your files anywhere in the world?
Does it offer Offline files feature that let you have access to the files even when you're offline and will automatically update the storage server with the most recent copy whenever you're connect to the network?
I think you are missing the point of a NAS for some people OP.
A NAS is not just a bunch of shared folders on a network. Optimally a NAS provides your many disks in some sort of RAID array that gives you a single share and some level of protection (whether that is duplication, one disk parity, two disk parity, etc.) for your data while serving that data on your network.
Anything above and beyond that- such as a sickbeard server, or a MySQL server, or a Plex server (just naming random stuff running on my NAS)- is icing on the cake. What matters is the cake, which is the shared array.
Personally, you couldn't PAY ME a reasonable amount to move my data from my Unraid servers to a Windows server. Why? Because there are many advantages to me that my Unraid servers have that a Windows server doesn't have related to my primary goals of a NAS. Heck just losing native SSH would drive me nuts.
With my Unraid servers you could take out the pen drive the OS runs off of and all of my disks that make up my array and move them all to a COMPLETELY different computer (different mobo, sata controller, GPU, etc.) and as long as the new hardware is on the compatibility list the system will start and bring up my array without any fuss.
No asking for activation or drivers, no needing to reinstall the OS, and updates and Flexraid or whatever. The system would boot, my array would come online and my content gets shared again.
I don't care what geewiz bonus features Windows can do for me. I care about as much content uptime as possible and an array that can survive a complete hardware migration.
To each their own, but there are real reasons to avoid using a Windows computer for a NAS.