First, the legal issue:
It doesn't matter what gun you carry, the fact that you were carrying a gun at all can be twisted to show that you were looking for trouble.
You carried too powerful a gun.
You carried too much ammo.
You carried too big a gun.
You carried too small a gun.
You carried too deadly ammo.
You shot too many times (because your less effective ammo didn't do the job).
You get the point.
The key to staying out of court is:
1) Act reasonably.
2) Be prepared to explain and demonstrate why you acted reasonably.
3) Be prepared to deal with the possible false accusations.
Many pplice departments, including the five largest ones in the country, encourage or require backup guns to be carried on duty. Many departments even issue backup guns. There are good reasons for this, all of which make carrying the backup gun explainable as the actions of a reasonable person.
Reasons for carrying a backup gun:
1) In case your primary gun malfunctions. ANY gun - or anything else made by man - is less than perfect. Glocks are the most trouble-free handguns on the planet and I had one break during an IDPA classifier.
2) In case your primary gun is taken away from you. It might be getting overpowered as happened to a deputy in Atlanta not long ago, or you may be facing too many guns to have any chance to draw your own. The backup will generally be smaller and better concealed, giving you more opportunity to wait until and opportunity to draw can be created.
3) In case your dominant hand is injured. I often carry my primary gun at 3:30 (belt buckle at 12:00) and my BUG in my left front pocket.
4) In case you run out of ammo for the primary gun. Generally BUGs are carried in locations where extra ammo for the primary gun would not have been carried anyway. I often carry 2 spare clips for my primary and still carry a BUG.
5) So that, given enough advance warning of a bad situation with insufficient opportunity to escape, you can arm a competent but unarmed companion.
Generally my BUG is smaller, less powerful, and less accurate than my primary gun, and if I haven't made it to cover by the time I have to reload, I am in deep doo doo to say the least. So, I am not counting on a NY reload.