Our team was very tempted to go for DD this year because of all the chain problems we've been having in years past (they have been randomly falling off, for example: last year we had 8 idlers and 4 chain tensioners and we were still having probs)

Then we saw 2 disadvantages to DD and we decided to stick with chain:

1. Set gear ratio/speed from gearbox (with chain you can change sprockets)

2. If wheel is damaged, the shaft/gearbox will likely be damaged too (with chain, there will be no further damage than wheel)