Well, I'm filling in my rebate about now. I haven't tried the Wifi card yet, cuz I don't have an access point yet. Instead, I bought it so I could be ok with any PDA with CF later on.
About future use, on the package, it says that there will be future support for CE 4. In terms of backwards compatibility, the device will work on Casio BE-300's, other CE 3 devices (Pocket PC/2002), and CE 2.11.