When we fired up the SPB Mobile Shell GUI on our Dual things fell apart more rapidly, the Redfly's screen going black and flashing up “New Screen. Out of memory”. And we needed to re-boot the Dual to bring it back to life after we unplugged it. All in all a little less than impressive.
Bottom line, the more bog standard your Windows smartphone the better it will get along with the Redfly though to be picky even here there are some minor issues.

Connections are limited to 2 USB ports, power and a VGA output
The text in certain control panels renders in some odd sizes, for instance open the WLAN setting tab and the words Current Configuration and Signal Quality appear in an enormous font and are thus more than half obscured by the relevant status boxes.
Also the image we had set as the background for the today screen on our TyTn appeared as a small box slap bang in the middle of the Redfly today screen. These sorts of graphical hic-cups may not be deal breakers, but they make the system look and feel just a little clumsy and half-baked.
Your opinion of the Redfly's essential day-to-day usability is going to be entirely based on your opinion of Windows Mobile because at the end of the day all the Redfly does is replicate it on a larger screen. It adds not one jot to the functionality or interface.
COMMENTS
Missing the point
Now, I'm no fan of this piece of crap (see above comments) but it does seem the "you should buy an Eee PC" brigade are missing the point some what.
The reason (Redfly thinks) companies are going to by fleets of these is because of the lack of risk. By keeping all the data and processing on the mobile phone, tucked safely away in Mr Big's very expensive suite pocket, it doesn't matter if they leave the laptop on the train, drop it on the airport concourse or have it stolen from their car whislst on holiday in Edinburgh They have lost nothing* because all the valuable stuff is still in their pocket and the Windows Mobile device offers remote wipe!
Yes, it would be cheaper to buy an Eee PC but it also increases the risk that the morons who use these things will go and give away all the company secrets.
Now, you (and I) may think that's an utterly moronic point and why not just implement over-the-air backup and decent security etc but, moronic or not, that is how they are trying to market these things so the Eee PC argument doesn't fly.
* where nothing = £330
This looks like bombing (in more ways than one)
Not only does it seem useless but US customs is likely to give you a "through" examination when you tell them that you laptop which "suspiciously looks like a laptop" contains no data and isn't a laptop.
Utterly pointless
Not only are you going to get laughed at for buying a crock of a WM phone to start with, but doubly so when someone discovers its not actually a net-book you are using, but its just something which blows up all the inadequacies of Windows Mobile on to an 8" screen. When they find out you've paid almost twice as much as what an EEE PC 701 now goes for, they'll probably give themselves a hernia from laughing so hard.
As Cobblers says, get an EEE or any one of the hoard of similar net-books, and use any phone you like as a modem. You'll have a fast, reliable system (if you go with the Linux versions), running Firefox and all the plug-ins which is a universe away from the hopeless WM browsing experience. Open Office is also vastly more compatible than using the crippled little WM Office apps.
