EI is nice for starting and smoother idleing. maybe less weight. On the other side of the coin you have to maintain a battery, switch that should be replaced every year if used a lot, and more wiring etc. Find a place to put it and so on. With glow all you do is tune it up and go. I have never had a glow plug go bad in flight. And they are cheap. Have had numerous problems with ignition systems over the years. I think it's just my bad luck. But EVERY ignition plane I have had either had an ignition box go bad or has had radio interference problems. And yes I followed all the proper procedures. Not one mag engine has ever given me problems. One plane with ignition even narrowed down to the engine itself. Every thing else in the plane was eliminated. And it took me 2 years to do it. I finally gave up on it and put in a Poulan on mag and never looked back, problem gone.
Another ignition plane would die every time I put it in the air with in a minute or less. But it would run till the tank was empty on the ground. I fought it for 2 years also figuring I must be overlooking something. I finally sent it back and got a replacement. That fixed it. For 2 years my Cub landed dead stick every flight. Never had to worry about refueling, it wouldn't run that long. Works good now though.
Another plane crashed on take off, not sure why, all I do know is the engine died. 25% scale Yak totaled. Sent the ignition box in to get the lead fixed and had to buy a whole new box, they said it can't be replaced on their model.
Have had a GP Giles 25% for several years now with a gasser in it. Last year when I put it away for the winter it was fine as always. This spring it suddenly has interference problems. Still does. I had it out today running it. Never flew of course. Now I have to try to figure this one out.
Not knocking any ones product. there are a lot of them out there working fine. Just letting ya know anything can cause problems. I just seem to be plauged with them.