Upgrade was not bad. I had thought that the new 2.1 wizard had some fancy upgrade utility, but actually it just directed me to go through Manager, as I've always done in the past.
The only thing that concerned me was that my 30-port digital station module wasn't recognized until I took the IP403 all the way to 2.1. I'm not sure if this was do to an improper power-up sequence or the fact that the DS30 was already at 2.0.
As sizbut said, 1.3 - 1.99 - 2.1