I would say you wouldn't notice any difference at all. There are two reasons this is done in aviation engines normally. One is for redundancy; if one system fails, the engine will continue to run on the other system, or spark plug as the case may be. The other, is that full size aviation engines have very large bores. It is preferable, and somewhat necessary to ignite the charge from two places. If you don't, the ignited charge on one side of the combustion chamber can cause a spontaneous combustion, or detonation on the other side of the cylinder, and/or the entire mix may not burn. Better to ignite the mixture in two places at the correct time, than have uncontrolled or incomplete combustion. That's a bit over-simplified, but I think you get the idea. In our small bore engines, I seriously doubt that you would notice any difference whatsoever in the performance or operation; spark plug or glow plug.

AV8TOR