I went with a Twin-sync setup on mine. LOVE IT and the installation was pretty straight forward. The biggest issue is getting the servo end points set up correctly so you get maximum sensitivity from the unit. I elected to put the sensor magnets in the spinner hubs. I am quite pleased with the operation and the engines are within 100-200 rpm of each other. One other HUGE advantage is that if you have an engine out, the active engine immediately goes to idle. Already saved my bacon on a touch and go.
http://www.troybuiltmodels.com/items/WRCTWINSYNC.html