Neighbor has had a twin for a 5 or 6 years now.  He likes his yeilds compared to straight 30's.  He does not look to be going any slower with his combine than anyone else, it may be more stressful than doing 30's, at least I know my 20's will make you pay more attention.  As far as meters I don't think there is anything else any better.  His field right by me looked like a perfect checker board with the twins staggered and the whole field looking like perfect spacing.  I run a Kinze finger unit and even after having the meters run on a stand don't get that good of spacing.

Gunner