Perhaps this will clarify the "mud": On 20 June Microsoft's Gabe Aul seemingly announced that MS would give away a free copy of the new OS to members of the Windows Insiders test program. Later (June 22) he "clarified" that statement to explain that testers on the Insider program will, like Windows 7 and 8.1 users, get a free upgrade to RTM on July 29th. However, to keep their version licensed, those that upgraded from Preview versions will need to stay signed up for future pre-release updates.
http://blogs.windows.com/bloggingwindows/2015/06/19/upcoming-changes-to-windows-10-insider-preview-builds/
I found that link a few minutes before looking here.
On that basis, I have burned the x64 Build 10162 ISO to a disk and installed it to my Dell D830 laptop, previously running XP, Core 2 Duo 2.2 GHz, 2GB RAM, (it was my Torrent box) and do you know what? It works just fine. I have got it to wake-on-lan and I can RDP into it, it runs Tor Browser and Vuze, and boots in 1 minute 5 seconds to a useable desktop. I have added Classic Shell for the Start Menu.
Installed x64 Build 10130, then upgraded to Build 10162 on Dell Inspiron 1525 laptop, previously Vista-32, Dual-Core T3200 2.0GHz, 4GB RAM. 64GB Sandisk SSD. It was my car's ECU interface & is now a backup for the tablet. It runs Win10-64 faster than Vista32 with the same hardware. Boot time is less than half.
Another older Dell desktop Inspiron 530s Dual-Core E2200 2.2GHz, 3GB RAM, 160GB HDD also upgraded to x64 Build 10162. It's a lot slower than the laptop because of the hard drive being slower. It's just a test platform. so not important if have to go back to the old OS (Vista).
My desktop runs a dual boot Win7/Win10. Haven't decided to keep it's Win10 going after the Win7 upgrade.
I still run Classic Shell on all Win7 & above.
I thing the "mud" issue comes from the word "Upgrade" as now defined by Microsoft. Many don't remember that there were 2 CD versions of Windows 95 & 98: Full & Upgrade. Upgrade was less expensive & required a Windows version to be already installed.