Forgive me for responding without reading the entire thread. I only read the first few posts and decided to say this even if it's already been mentioned.
The most important thing you need to consider before making this decision is that employing a mouse gun to stop a threat - as with any gun - is using deadly force, and that fact will remain true regardless of how you use it. In other words, you can't choose to shoot a guy in the leg and then say it wasn't deadly force. You used a gun - it's deadly force. End of story. On the other hand, using mace to stop a threat will
almost never be construed as deadly force, except under the most specific and convoluted circumstances (you sprayed a feeble elderly person who was wearing an oxygen mask and towing an O2 tank, or something equally ridiculous).
The point is, they aren't interchangeable. You can use mace to ward off a threat, real or perceived, and defend your actions with far more ease than if you use a gun to defend yourself. Also, should you be unsuccessful in that defense, the repercussions will be enormously different depending on which tool you employed in said defense. If you shoot someone and later fail your attempt to defend yourself through justification, you're going to prison for several years, or longer. You spray someone with mace or OC, and fail to defend your actions, you might get fined and spend a couple months in jail for assault.
All that said, if I was forced to choose between carrying a tool which allows me to employ deadly force, and a tool that allows me to employ less than lethal force, I'd choose the former. I've been sprayed with law enforcement grade OC in an LE academy, and also been exposed to it in the field when it was directed toward others. It's certainly not pleasant, but it is NOT a reliable way to stop a threat.
