Unless you ride like a complete demon you should easily see 50 mpg, thats what I'm getting in my DCT. The AT is a good commuter, nice bit of height to see over London's traffic, I used my XRV 750 thus for years.
BUT - whilst I no longer commute I'm glad as I have the DCT and I find it's slow control (really slow, 1-5 mph) hard to manage, I wouldn't want to be squeezing through traffic down the A13 like I used to on my manual XRV.
I love my DCT, but having ridden it for a while now (1,000 miles) I would have gone manual if still messing with heavy traffic daily.
Take a very decent test ride is my advise and make sure you replicate the conditions you will encounter when you do.