Windows 10 Pro OEM - works great!
Although the eBay description I purchased from didn't specifically state this, it's an OEM version. Buying an OEM version of Windows is usually much cheaper than paying the full retail price, while it's basically an identical product (with less flashy packaging). The main downside of OEM versions of Windows is that they are tied to one computer and set of hardware and you may not be able to reinstall it on another computer in future when you upgrade or replace it, so be aware of that.
It's designed for installing Windows on a brand new computer, but I was able to also use it to upgrade my Windows 10 Home to Windows 10 Pro, although to do so I had to first upgrade to Windows 10 Pro TRIAL version (using a publically available licence key found online) and then convert it to the full licenced version using the key in the purchased package.
That worked beautifully, and I would gladly use this method again in future.
Verified purchase: YesCondition: New