Where have you read that. I would like to read it. I looked at them but decided to use GE.
The darton has a small groove around the top and a series of small holes. I believe that this design will hold more heat and could possibly cause turbulance with the coolant.
The GE's on the other hand look to be more open at the top. I wish I could have got dimensional information on both of them. If so a calculation of surface area at the top of the sleeve could have been made and see if they are close or not. Picture wise I do not think so.