This is certainly a convenient, and cute, way to get from market to market in Cologne. We boarded the "train" right next to the TI, adjacent to the Dom.
Some drawbacks: the ride can be extremely bumpy since the cars seem to have no springs. Too, we were stranded at the Angel's market (Neumarkt) when the tram folks had packed up shop with about 1 1/2 to 2 hours of market time left. And they don't stop at the Rudolfplatz "fairy tale" market at all.
Enjoy your time at the markets!