You can't legally split the MS family pack with someone not in the family (or household technically).
Fact: unRAID offers a discount if you purchase 2 licenses, Limetech is OK with you purchasing the two licenses and splitting them with someone other than yourself. This "can" lower the cost. Nothing more, nothing less. All you have to do is accept that in some situations it is a "pro/plus". The hassle is up to the individual, and it doesn't apply to everyone since some people build multiple file servers thus they realise the discount without the hassle, or they split it with family which can sometimes be painless.
It would be like someone saying that FlexRAID built on top of Windows is a plus because you can run any app that windows support, then having someone suggest:
* you can run windows in a Virtual Machine or hypervised
* it's a file server you shouldn't be running apps
* all the apps they need are available
* windows is a security risk bla bla...
... so it's not really an advantage.
We should just accept that FlexRAID is good when absolute flexibility is a desired outcome and unRAID is great if you just want a simple file serving appliance with the option for flexibility and usually lower than the cost of consumer NAS with lots of drives.
The OS residing on a USB stick is also a "pro" to many people since it leaves more drives for storage (you can't include the OS drive in your FlexRAID pool). Just because you have enough ports, doesn't mean that if you were provided the option of running FlexRAID via Windows-To-Go USB key that nobody would want it. I'm sure many would. Myself personally, I don't care about the USB aspect in my current server because I also use this file server to download, fetch metadata, active directory services, wsus (and planned VM for pfsense or something of that kind) and so I would not benefit from the OS being on a USB key.