The pro version is a good midway point between the slightly restricted Home Version and the full on Enterprise Version. The only question I have is this: what are you trying to upgrade from ?? Are you trying to upgrade from the Home version or from a previous system like Windows 8 or Windows 7 for that matter?
If you are upgrading from Win 7 or 8, you still can do the free upgrade with your serial key you already have (I have tried it not long ago and it still worked. I guess, MS wants to have everybody on Windows 10).