Has anyone used Microsquirt for the 420a engine?
From what I've read it's basically a fully assembled Megasquirt 2. I'm about to pick one up, and start the tedious project of learning how to code (I mean tune).

Nope, I have personally never heard of Microsquirt, only Megasquirt.

it's just a physically small version of megasuck in a small plastic box with a real connector instead of the stupid printer port.

Megasquirt honestly isnt all that bad orf a platform with not much else available. It's pretty widely used in the Miata world. It does sucks that you have to use two different programs to log/tune but you get over it.