DD = direct drive It uses a slightly larger motor.I think its a GWS IPS50 or 100. Sorry I forget.
I was thinking because of the largr motor and the fact that it can take a little more current that it might have a longer life soan than stock tail motors. It MIGHT be a little longer ,has pretty good tail authority but it still burns out pretty quickly. You use the stock motor mount, buy a GWS motor and prop and a special prop adapter. The money diff. between the DD and dual motor isnt a lot so your better to go with the dual motors. BUT if youre planning on staying with the stock battery and motor then DD is a good upgrade I think

Dual motors live longer cuz they split the current. If youre running an 11V battery then this is the way to go for sure. You need a special motor mount that allows 2 motors to be mounted on it.You keep the stock tail rotor and gear. When you wire it theres 2 ways.
Red wire from the 4 in 1 goes to a positive post on 1 motor.then run a short wire to the positive on the other. Then the negative wire gets hooked up the same way on the negative posts.

Theres a website called blade cp repair. Im not exactally sure of the address but they show how to hook up the direct drive setup and may even explain it. Ill post the site if I can find it.Ill try get a pic or 2 of my dual tail setup just after lunch.Gotta go get batteries for my camera