Well I have just gone through the moving hardware process. It is not smooth. The free upgrades are definitely device locked.
On my old PC I had a Win 10 Pro installation upgraded from Win 8 Pro (Retail) and so activated with a Digital Entitlement.
First I removed the key/activation from the old PC with the command: slmgr.vbs /upk
This uninstalls the licence as required by the T&Cs, but doesn't "reset" the hardware fingerprint on your original key.
I then performed a clean install of Win 10 Pro (TH2) on my new PC using my Win 8 Pro (Retail) key. It installed OK but didn't activate (Error code: 0x803F7001). The servers know the new PC hasn't be activated previously and that the Win 8/10 key is associated with different hardware.
So I tried automated telephone activation with the command: slui.exe 4
This is the normal route for moving a retail key. However this fails.
So I then jump onto MS Chat Support and explain the situation. I give them my Win 8 Pro key and they confirm it is valid. Agent says they need a remote desktop session. They check a few logs and try removing and re-adding my key which still fails. They then run a script which injects a key and activates the installation. This was only on screen for a split second but I saw it was a
different key. I ask them about the key and they said it's all fine you are activated know we fixed it for you. I ask them outright for the key because I saw it was different. They say they will have to call me to discuss, which they do. After a brief chat they (painfully) read the new key out to me (this is not the generic Digital Entitlement key). In Activation it now shows as Product Key rather than Digital Entitlement.
After the support session ends (40 minutes in total) I extracted the new key from my system to confirm it matches the one read out to me. I then also note the product type,
OEM:NONSLP
So they have given me an OEM Win 10 key as a free upgrade from retail Win 8. They have allowed me to move the licence as per the T&Cs but it is once again device locked. All I can say is good luck trying any of this once the free offer ends!