@pipsypop
Cafe Au Lait are really over priced most places. Ever since Martha Stewart raved about them they have been super popular. I have seen them as high as $30.00. In my opinion there are a lot of much nicer dahlias out there (for 1/3 the price)
Your tuber looks just fine. It has an eye that should grow just fine.
I have had dahlias grow to 6 ft plants with multiple stalks from tubers half that size.
The ground is still a bit cold where you are, to plant it outside, so you might want to put it in a container with damp (not soaking wet) soil and get it started. It won't need light until it emerges from the soil.
Plant it outside about the time you would plant tomatoes & you should be golden.