I think the only difference is that WU allows upgrade to 10 from Windows 7 SP1 or Windows 8.1 Using the ISO you can upgrade from Windows 7 without SP1 (as long as it is activated) and Windows 8.0 without required to upgrade to 8.1 first. Of course you can burn the ISO to DVD for troubleshooting, as well as using it to upgrade many computers without having to download each time. Another difference is that the ISO (from Tech Bench) supports both Windows 10 Home and Pro, depending on previous Windows version or serial (for clean-install), while WU will give you only Home or Pro. I don't remember any other difference. I vote for ISO.