Mags work great with the following areas of exception...
They have a weak spark at low RPM inherent to the design. What that means is loading up during extended periods of idle if your mixture is at all rich, fouled plugs, etc. (I've been through this with my turbo motor). Ok for race boats. Not ideal for extended idle situations like marinas and stuff.
They also use a little horsepower to turn them since they are a generator. I forget the number but it's negligible.
Once in a while the magnets have to be recharged. But other systems have issues occasionally too so I don't view that as a liability only on a mag.
Unless I had a used one I wouldn't go that direction spending the money from scratch. I'd put an MSD distributor with a Crane Marine 6 box and forget it. Lots of reliable voltage potential, clean idle, rev limit built in, bitchin distributor.
Just my .02