I agree the MegaSquirt 'site' can be overwhelming for first visitors. The fact they (some dealers) still have all 3 upgraded ECU-versions available, and even more smaller versions and some 'pro' variations, isn't helping keep things clear what you actually would want or need.
Autolearning kits are just that; You install, They learn..., and leave the user fairly in the dark of what really happens 'under the hood'.
Perhaps great for the 'I just want to drive (to the sat.night meet and pull out the lawnchair)' folks, but anyone who likes to tinker with their engine tune and get more/most out of it should like to explore new grounds/learn new ways of improving the old.
For elaboration, here's a small (and kinda boring) compilation video I made over a week ago which shows some of the things happening possible with the ECU.
I've got a few posts on my homepage going slighlty more indepth, shown below in chronological order;
The last link explains a bit how I installed the ECU in the car, which actually 'tells' HEI 7-pin module when and how to spark to the coil.
I'm using a stock 'Lean-Burn' distributor to provide the trigger for the HEI-module and ECU.
