Until now the major difference between the two - Field Coil and Permanent Magnet, was that the FC design meant that the alternator would only supply what was needed, and would last for absolutely ages, it being under-stressed most of the time. The PM design with a shunt regulator was effectively working under full load all of the time, and whatever current wasn't being used by the bike's systems was being shunted back into the stator windings, adding to the stress by raising winding temperature. Sooner or later, the stator insulation broke down, which is hardly surprising, given it's in a very hostile environment to start with.
However, the advent of the series regulator now puts the PM stator on a more-or-less equal footing with the FC alternator - the series RR only passes what is needed by the bike's systems, but crucially the excess current isn't dumped back into the stator, the demand is simply cut off. It took many years for a decent design to emerge, as the necessary semiconductors to build a reliable quenching and control circuit weren't around to incorporate into a mass-market item. The Big Bogie there was the back-EMF that occurs when you cut off a generator coil.
The idea of series regulation isn't new - it had been tried decades ago, but was never successful at any price ordinary owners were prepared to pay. Compufire were the first I knew of to offer it for retro-fits at sensible money, and in the last couple of years, it's emerged that Shindengen have been quietly supplying one to Polaris for several of their ATVs, with another, heavier-duty one now on the market.
Currently, I'm running one of the Shindengen SH-775 series RRs, with one spare just in case. I have deliberately chosen to use it on an elderly stator that would certainly have failed by now if it were still connected to a shunt RR. So far, so good.