So to get back to the 1M, which "proper" flash tune seems to be the best available option for a stock 1M Coupe?
Not limiting to US tuners here - Kelleners, Dahler, Lightweight.
Preferably a tuner with a handheld device that allows for getting back to the stock ECU quickly.
@Biglare is running an ESS and seems to be pleased with it - he's also showing significant power gains with 390PS with a stock cooler.
It's difficult to compare by just going to the tuner's websites. It would be good to have a proper comparison such as the autobild tuner comparison
http://www.daehler.com/docs/Daehler_1erM_ABSC.pdf