I once asked Fantom about this as well - they are all the same machine, first coming out in plain alum color, then blue, then red, but all the same product but for color. All the color can tell you is the relative age of the dyno.

I don't believe the software has been updated in ages - the latest version is at www.deccosoftware.com. Last update I believe was going from DOS based to Windows based many years ago - it still runs fine on Windows XP. Most computers now don't have a serial port, but it functions fine with a serial to USB adapter such as made by Belkin. (And if you are a Mac fan, yes, it is possible to run it on the newest Intel based Macs under OS X using a Parallels virtual windows machine and a Belkin serial to USB adapter) (I'm a new Apple convert).

As far as buying one, I like mine, still gives good info, and you don't have to worry about any variation in results due to the condition of your slave motor - the flywheel dyno's have no slave motor.