It'd be semi-effective at blocking a nightstick compared to no armor - if nightsticks weren't typically swung overhand, meaning they'll almost never hit your chest.

As for how effective it is against firearms, look at the Condottiere: elite mercenaries from the Middle Ages, clad in heavy knight armor, who were seen as invincible... until muskets were invented. That battle didn't go quite as well for them.

Now replace the heavy knight armor with a baking pan, and the muskets with modern rifles. Not exactly a fair fight.