I had enough MSD equipment fail enough times on me that I gave up and started doing the HEI upgrade instead. Ignition performance at least equal to MSD, cost and price much lower, reliability much better.
Ran a basic Pertronix in my '65 Mustang six for 10 years with no problems.
Going to try this Pertronix II in the SS mainly because it was convenient and stupid simple to install. That's really appealing to an amateur like me. :o