It varies whether u should mash it out or not. Anytime ur gonna u2 after it, do not mash out as hurts the damage scaling(and also makes it impossible to do walk or dash u2 midscreen). If you intend to do ex dreads after it then you should mash out as it will give u more damage.
The trickiest choice is whether or not you should mash it out if ur gonna do upkicks after it. Mashing ex mgu and doing medium upkicks gives u slightly more damage than a mashed fierce punch mgu. Mashing ex-mgu and doing heavy upkicks gives even a little bit more damage than that. Not mashing ex-mgu and doing heavy upkicks can give u the most damage cause the upkick can hit twice. The problem with using heavy upkicks is if youre too far youll whiff and get punished when ur opponent techs, and it is harder to hit on some characters than others. Personally I usually mash and do medium upkicks so that I dont have to worry about getting punished if the upkick misses.