200 hours on a factory-new O-360. Before first start I ripped off the right mag and installed a P-Mag purchased used from a fellow VAF'er. That P-Mag had just been back to EMagAir for software update to the latest at that time (V40). Lo and behold the P-Mag suffered an infant mortality within the first 15 hours of operation, necessitating the replacement of the main electronics board at my own cost which was not insignificant.
There - that's the down-side of P-Mags in my limited experience.
Now for the up-side. Easy engine starts in all weather conditions (literally -20C to +35C). And the real bonus... I see fuel consumption figures that are, on average, 1gph lower than the Lycoming power charts indicate.
Would I install a second P-Mag? Well, that depends on its cost, and on what other options are available and the cost for those options. I would like to ditch the impulse coupling on the Slick magneto mounted in the left hole, but not at any cost. I likewise don't want to have to install another entire electrical system to power an ignition system.
One has to make the decision regarding ignitions with one's eyes wide open and with a full compliment of information in hand.
At the moment I'm leaning toward an SDS CPI2 ignition system for the left side with its power coming from the primary electrical bus with the self-generation capacity of the P-Mag acting as my "get me home" fallback plan. Still, I don't see the cost justification and won't until I'm facing a bill for the 500 hour Slick inspection.