Can't say as I agree on the idea of Mace or pepper (OC) spray. Btw, of the two, OC spray is superior to Mace.
OC spray generally comes in one of three delivery types: fog, stream, and foam. If you use either the fog or the stream, the air recirculation will contaminate the entire cabin. You'd better get your full-face masks on...
The stream and fog are meant to be used at a distance of 5 to 15 feet. The propellant (usually alcohol based) evaporates quickly, leaving the pepper on the assailants skin. If you are too close to the subject (or spray too much), the propellant won't evaporate, so it sort of "insulates" the subject from the pepper, reducing the effect.
The foam types can be used indoors, but a clever perp pull the foam off his face and fling it back at you.
I just don't see OC spray as being useful while grappling with a knife wielding attacker, particularly one who is determined enough to commit suicide. I've been exposed to OC spray, and while it certainly isn't much fun, it's not going to stop someone from slashing away at you. If you're determined enough, you can continue to fight even though you've been sprayed.
OC spray is fine when some university students are staging a sit-in and don't want to leave. They are relatively static, you can deliver the spray from a stand-off distance, and they're not determined enough to endure much pain. But OC spray is not very useful when fighting a knife-wielding subject in very close quarters.
OFBSLF