Crane, Mallory, Accel, Hot Spark, Pertronix and I am sure there are more make these Chingaderas that go into the stock distributor. From all of the reviews I could find, they all use the Hall Effect, magnetic pickup except for Crane which uses an optical sensor. Reviews say optical sensors are inferior. The Mallory and Pertronix distributors basically just have those modules in them, I suspect that's what Tom is doing too. I know that's what Jason's setup is. The higher end ones have rev limiters incorporated in them, but those don't appear to be available for our 6 bangers.
I may be wrong, but then it becomes a matter of brand and what you feel is the most reliable. GM? Mallory? Pertronix? Tom Langdon? Etc etc. So, now I see why this is such a subjective subject. Because they are all basically the same? I like the stock look, so I want the coil separate. That narrows my choices a bit. I guess if you purchase one pertronix module and one to go on, you will have the spare parts you need in case of a failure.