I think Josh and I both agree that whatever the solution, it would be nice if the MS2 and derivatives had just a couple more inputs and outputs.
I like MS3 as the software has more options, not necessarily the fully loaded MS3X as it is probably overkill for most.
Really my preference for the MS3 surrounds the hardware/software enabled by the faster CPU. It's new. It's hip. If you want to run AC control, there's a menu. If you want to run fan control, there's a menu. There's actually a lot of menus, for better or for worse, more than MS2.
The versioning system is a bit ambiguous too:
Megasquirt - currently supported
Megasquirt PCB: v3.0. Hobby through-hole component version. Pretty much everybody uses this or a 3.57
Megasquirt PCB: v3.57 is the surface mount version, virtually identical but not offered as a solder-together kit
These are functionally identical. Both have the same clunky 37 pin connector which I think is not a great choice.
CPUs - plug in to either of the above PCBs
Megasquirt v2: 24MHz HCS12 CPU, serial only communication
Megasquirt v3: 50Mhz MC9S12XEP100 CPU, native USB and SD card logging. Needs a bigger box though.
Megasquirt v3 with MS3X: An add-on card for Megasquirt v3 that gives you a TON of inputs/outputs, individual injector drivers, individual coil drivers.
Microsquirt
Functionally similar to MS2, but in a proper enclosure and a real harness connector. Small, weatherproof.
Microsquirt but repurposed as an IO-box?
Getting weird in here isn't it? If you have an MS3 CPU, you can flash a different firmware and connect an MS3 to a Microsquirt module for additional I/O
https://www.msextra.com/product-rang...squirt-io-box/
This might be better than the 3X add-on as you can drop it on at any time via the 2 wires of the CAN bus.
MS3-Pro, MSPNP and a whole bunch of OEM and engine specific boxes
MS3X in a proper enclosure with a real harness. Or MS with engine-specific options are for LS motors, certain Fords, basically intended as plug & play ECU replacements.
TBH these dangerously close in price to commercial solutions and probably of limited application in the DeLorean.