Hi Nimrod,
It is likely to be quite involved to connect the Phaserunner MT to the Magic Pie Edge, and you would need to make up a plate for the controller housing to replace the original controller, unless you are prepared to destroy the original controller in order to just use the main heatsink casting.
I suspect that the Pie's original main harness
(or motor harness) would need to be cut and modified to connect to the Phaserunner MT controller, but this is unlikely to be straightforward.
I also noticed the following on the Grin Tech website:
AVAILBILITY NOTICE: As of Sept 2021, we are completely sold out of all Phaserunner_L10 and Phaserunner_MT motor controllers, and due to the global semiconductor shortages we are unable to secure more circuit boards until late Summer of 2022. We apologize for this supply disruption. When we re-introduce the device, it will be an updated V4 model that matches the plug and connector standards adopted with the V4 Baserunner Units.
Although I'd really love to have the variable regen function, I can't justify the amount of work
(and additional cost) that it would entail.
Alan