I have one of the Electroair units and one conventional magneto.
Since my airplane's engine has always been configured that way, I can't give you a before/after comparison, but I will give you a few points to consider:
1) The engine starts much more easily on the EI or the EI and Mag than on the impulse coupled mag alone.
2) The engine runs much stronger on the EI alone than on the Mag alone.
3) I have suffered one failure of the EI system. I was headed to SnF about a month and a half after the first flight of my airplane. On run-up, the EI was completely dead. Jeff Rose, who developed the system and was the support network for the system, was at SnF and couldn't be found to diagnose the problem or send replacement parts, so I missed the entire show. If my mag had died, I could have sourced replacement parts (or a whole new mag) in a day or so and made the show.
The point is, you won't find the support network for a low volume EI system like exists for our mag's. That means if the EI breaks, you may be stuck somewhere for a few days or a week.
By the way, I've had 400 or so trouble free hours since the EI failure.