There are certainly lots of opinions out there on this subject.  For me, I like the idea that the backup doesn't even require electricity, let alone electronics.  I use a vacuum pump and old-fashioned gyros on my non-turbocharged plane.  If it were a turbo recip I designed a pressure regulator that taps off manifold vacuum and compressor discharge pressure to create a steady source for the gyro - no pump required.  In the case of a PT there is a constant source of air pressure available, so to me the answer would be obvious.  Whatever the reliability is, the result of a lightning strike can be random - you could loose all electronics or just a few, no predicting.  Not going to go near a lightning strike?  Yeah, right.  I think the idea of a battery backup works a lot better if the backup system is always disconnected from the main system.  That means you would have to leave it off until you needed it.  I don't think I like that idea either.