cheseroo said:
I have heard stories of the Pertronix unit burning out if you leave the key on for extended periods with the engine not running.
Indeed Pertronix warns against doing that.
I had the opposite experience with my current TR3; installing a Pertronix made it harder to start. Root cause was eventually discovered to be a bad battery (letting the voltage sag while cranking), but with points the engine would start and run fine even with the bad battery. (Until it got much worse, about 6 months later.)
I have had similar experiences with the Allison unit on my Stag (similar to the Crane XR700), where sagging battery voltage (due to driving without an operational alternator) caused the engine to just stop running rather than gradually degrading as it does with points. By my way of thinking, that makes the car less reliable overall (in terms of getting home under it's own power in spite of the bad alternator, as opposed to coming home on a flatbed).
Bottom line, IMO, they are good for reducing periodic maintenance, but not especially good for overall reliability. And it just isn't that hard or expensive to throw in new points and condenser as part of a major tune-up.
Performance wise, I couldn't tell the difference switching between fresh points, Pertronix or Crane XR3000. The XR3000 (which is a capacitive discharge unit) might have been fractionally easier to start in wet weather, but we get so little of that around here (and I try to avoid driving the TR in the wet anyway) that it just isn't a consideration for me.
The MSD 6 that I ran for many years on a former TR3A did seem to improve performance slightly (especially starting), but it had its own set of problems (including burning up the center contact in the distributor cap and drawing nearly 10 amps).