The Ultimate Detailing Towel looks like another spin on the WW people use for drying their vehicles. The Concours Buffing Towel looks like a killer towel you'd use to buff off your polish or wax. I guess you could say the UDT can do anything the CBT does and a whole lot more. But... this isn't to say stock up on UDTs and skip the CBT. The CBT could be considered a premium buffing towel. Maybe surpassing the best MF towels currently available. The CBT is not cheap, but with the 60 day money back guarantee, that's saying something about the high quality you can expect.
This is based solely from reading the description of both products and enlarging the pictures for a better look, not from first-hand experience.