You are correct - the 3.2" itead screen I have only operates in 16 bit mode but the Sainsmart ones can operate in 8 or 16 bit mode.VaultBoy I've seen a 3.2 that works in 8 or 16 bit mode, it may even have been one of the sainsmarts, so I assume that one would work on the UNO if you need it to.
That being said, I have found it a bit of a pain using the UNO for 2 reasons:
- the screen + touch panel uses up nearly all the pins which limits what you can actually use it for
- there is a problem with the bootloader on the UNO which, in some instances, means that you only have access to just over 28k of program memory rather than the stated 32k