Here is what I did.
Upgraded from windows 7 sp1 to previous build, then upgrade to windows 10240 build.
Choose stop receiving the insiders build, it did one reboot
Got the key from showkey
Then I left insider program via insider website
Remove all device except the 10240 build from my my account
Created an ISO from ESD build 10240 using Kari instructions
Created a bootable usb disk using windows 7 usb boot creator.
Did some partitioning
Installed Windows 10 and it took the key without issue but it was a little slow checking it. It took about 30 minutes to install. It activated with no expiration date at all. I also logged into my Microsoft account. I also opted out of most privacy setting except for location for the apps.