The only thing I've noticed that my car is in regen is the lumpy idle. But whenever I get "on the gas," there's never any stumble. And as I've mentioned many times in previous posts, my car feels like an absolute rocket when in regen. Instantaneous turbo response at much lower RPM than usual, a much bigger swell of torque in the mid range, and more persistent power at higher RPM than usual.
After my first oil change back in September, when they also performed an engine software upgrade, regen seems to happen way more often, and I love it.