For me, the main con has been the price to get one. It just hasn't been worth saving 5 min at tuneup time to check/adjust points and timing.
The other con is that it does consume more power from the bike's electrical system, particularly if you go with the 3 ohm coils. Why should I care?
Well, except for the 650s which I know little about, the SOHC4 charging system doesn't have enough omph to power the electical load and charge the battery at idle speeds. So, increasing the electrical load means you deplete the battery faster at those RPMs and you have to rev your engine higher to overcome the load and begin charging the battery. Operationally, if you spend most of your time in cruise or at RPMS above 3000, there is only the decrease in battery longevity to notice. If, however, you are in slow city traffic, and stopped at lights idling most of your operational time, the battery can steadily run down. This shortens battery life considerably, as the more time the battery spends at less than full charge, the shorter it's life. I do mostly city driving and it is hard enough to keep the battery peaked without adding more electrical load.
I'll let others list the pros, as I have never owned an electronic ignition for the SOHC4.
Cheers,