My buddy who has a hot rod BBSHD is much happier with his external ASI controller than he was with the rootin' tootin' overdriven Luna controller. Not only does it give him dramatically improved (and more tunable) performance, but he no longer has to watch the temperature like a hawk (because the controller's heat isn't being piled on top of the motor's heat).
Me, I like to drive things within their ratings. If I want more power, I'll use a more powerful motor rather than burn down a less powerful one.