I have moved on from Belt Drive and Idler Drive, but still retain these TT Drives to use at my leisure.
I also have the opportuniity to listen to a SME Belt Drive, Linn Belt Drive and Garrard and Lenco Idler Drives in other systems.
Today I use a DD as my main TT and others I know have swapped out their Belt Drive TT's to be superseded by DD in their systems.
Taking the Drive out of the equation, there are other areas where the DD wins over.
The DD has in many cases especially on the models being refferred to, exceptional speed control built in.
Other Drive systems can cost much more to achieve a speed control that is with similar desirability.
An Idler Drive can easily have a Standalone Speed Control that commands a $1000+ and Belt Drives have had many add on ancillaries to improve Speed Control at similar asking prices.
This is one of the reasons I became interested in a DD.
After hearing a DD in A/B comparisons to a owned and well respected Idler Drive,
I became a convert to the DD and have not looked back.