Well, you are very much correct on the watts/performance issue, I look at it this way. Your average PII/PIII is about as powerful as some of the ultra-efficient Arm-based SBC devices now available for Linux users. If TDE can run well on PII/PIII hardware, then it will likely run well on those very efficient Arm-based systems as well.
I don't run the PI and PII all day. I use them because they provide a nice way for corner case testing. For example, a while back I noted problems with the logout status dialog because only the PI or PII would show them.
Darrell