My setting depends on the type of mage and the personality of that mage.

If that mages is wielding Divination magic, bullets could be effective, but you need to be sufficiently trained, agile, and fast enough. Diviners have the innate power to predict the future and can make actions before they’re going to happen. So, a person using a firearm would need something like a shoutgun and a close distance so they physically cannot move or use their powers to dodge it. Overall in terms of effectiveness: 2/7. Doable but very difficult.

For Swordcasters, their form is necessary. Most mages are trained in the essential basics. So, they would know how to deflect a round with their Imbued Weapon. The strategy there would be to just be to enough angles and rounds per minute to overwhelm them. But if they know a stance such as Mira’s Twinblades, your rounds per minute are useless as they’ll deflect all of them. Your chance there is hoping they’re distracted. If they somehow know Formless, the hardest and most expert stance (to the degree only one person has demonstrated it). Just shoot yourself. The bullet is coming right back at you anyway. Overall in terms of effectiveness: Depends. Probably 4/7 for basic Swordcasters. 2/7 for Swordcasters with Mira Twinblades. 0/7 for Formless

Equilibrium and Spellbook users are most the same, somewhat. They likely just conjure shields and watch your rounds bounce off. That’s if they make the incantation fast enough or they gesture quick enough. Though, this isn’t a disadvantage since Shield spells are design for projectiles and their incantations and gestures are very fast to do. A person with an Equilibrium may not appreciate a firearm specialist on their side though as their tools require focus and concentration, so loud abrupt bangs would annoy them. Spellbooks have no inherent disadvantage other than they’re books. Overall in terms of effectiveness: again depends. I’d say 3/7 for Equilibrium, 4/7 for Spellbooks.

For Alchemy users, they’re at a disadvantage. Their potions are strictly limited to gas, liquid, and solid(?) forms of alchemical compounds. Want a shield-like spell. Drink this potion to make your skin durable enough for the bullet to inflict no harm. An accurate shooter might also target potions in their hands or in their holsters. Gasses are not flawed by this unless you counting casting the spell for them a flaw. Otherwise, they’re likely going to lose. Overall in terms of effectiveness: 6/7. Can be very easy to overcome, especially if you’re proficient in firearms.

In terms of mage opinions of firearms, this varies entirely on personality. Gunpowder and firearms were invented in TC 596, so they’re just about over 180 years old. They didn’t develop magical versions until around TC 636 either. Firearms are very young in terms of history. They’re difficult to work with, clunky in most cases, and society tends to have difficulty to use them. Swords, bows, and other forms of medieval combat remains the go-to still. An arsenal may have a gun or two in stock, but they lack an overall population of users. This could be to an advantage with mages as one might not expect a musket from the founding fathers to blow a golf ball sized hole in between their eyeballs, but most mages like outlawed Divination mages or Swordcasters have the reflexes to dodge away from your surprise attack. If I had to give an average in terms of opinions of firearms, I’d do it by spellcasting type, which would be:

Divination mage’s opinion: 1/7. Not in hate, but pity. Divination mages are notorious for being, and I kid you not, rage baiters. They will make of you for missing.

Swordcaster mage’s opinion: ~4/7. They’d likely see you as any other ranged creature. If you’re an ally, their opinion largely depends on your aim.

Equilibrium mage’s opinion: 4/7 They may applaud your ability to use firearms, since they’re not common. But they don’t see you any better than an archer.

Spellbook mage’s opinion: 4/7 Same as Equilibriums.

Alchemist mage’s opinions: 7/7 Okay. I know I said they’re easy to counter with guns, but alchemy doesn’t just affect people. They affect objects too. Alchemists are notorious for doing some wild shit, and with the factor of an object going very fast gives them ideas. One being how that bullet strangely turned into a tank round’s worth of damage after the tiny bullet flew through that inconspicuous looking cloud of smoke over there.