Milord Cooldown and nuclear option are just two different levels of safeword. Unless you do not trust yourself to not abuse your safeword (and thus need the threat of a ruined keyholding relationship to prevent you from using it too eagerly), a simple safeword for "unlock immediately and talk about the future of the arrangement" will do.
None of that replaces the emergency key though. You need that in case you ever get into a situation where you need the belt off for whatever reason (e.g. medical emergencies, trouble at security checkpoints or whatever) and your keyholder is not available at moment's notice. Having to wait for the belt to be cut off increases your long-term health risks and destroys an expensive item in the process.
