I may be wrong but... my take is that a db is basically used to go "downstream" with some direction supplied by oars. Sleds go upstream, generally with jet power.
The prop on a db is fine for holding in a deep slot or bactrolling but the db design doesn't lend itself to providing good tracking.
There is a great deal of diference between sled designs but the difference between sled and db design is huge.
Figure out what you want to do with a boat then find the boat that can do it.