Originally Posted by buckf1tches
This did work! I noticed that the ROM wasn't exactly like what comes with the phone when we received it from Verizon (which was the same day). I am basing this off the type of wizard that opens when you first turn on the device. It wasn't rooted, though, and did put back what appears to be a stock ROM of 2.1. It's going back to HTC/Verizon tomorrow.
There are no customizations in this ROM - period.
The "stock" setup screens certainly changed between 1.5 and 2.1, and may have changed slightly from the original HTC/VZW 2.1 OTA to the July 2010 2.1 OTA update.
Having said that, there is one other thing that you might have noticed: you didn't see a device activation screen during setup. That is because NONE of the dev ROMs here on the XDA Eris touch the activation state of the phone - including Flashback21.
If you want to deactivate your phone, you need to perform the Factory Reset process from the OS menu, and a "stock" Eris recovery must be on the phone. (So, if you desire to do so, go ahead and do a Factory Reset after you have installed Flashback21)
If you have already turned in your phone, then no worries - the carrier usually deactivates the phone from their side.
Anyways, that's probably what you noticed. Flashback21 is completely stock.