I have an electronic parking brake on my new daily driver 2022 Ford Maverick. It's fine in a hill hold parking situation, but I dont know how it will work in a loss of main braking situation. I suppose since this vehicke is fully integrated it will allow you to pull up on the park brake button and vary it to "pump" the E brake to slow down, but that may be because its integrated electronically to the rest of the vehicle, and probably required by DOT regs to sell the vehicle in the first place. If you were to do that to a vehicle not programmed for that, all you may get is on/off.
I am currently researching doing this build, and honestly think a mechanical cable parking brake makes the most sense from a simplicity standpoint. Additionally with a loss of braking from the main system, you can "hold the button in" on the handle and pull up on the handle to "pump" the rear brakes to stop. Since this is a "kit car" it's essentially a fairly well engineered science project of sorts. The K.I.S.S. method is best. DF offers a setup that uses solstice/sky calipers and cables which is probably the best and more likely bolt on solution.
Matt