What do the users of electronic ignitions think about their units?

Are you using dual or single with a mag?  Is everyone using Light Speed? 

The main reason to get one is to be able to advance the timing at around 7000 feet and above for more efficient engine operation.  Has anybody compared both side by side -- with electronic and without? 

When you're running an IO550 LOP at altitude, is the savings really as high as 1 GPH for the same HP?

David T