The brake cleaner is a degreaser exactly like the avio gasoline. Indeed, I would say that they are the same thing judging by the smell and the color or at least they are the same thing the avio gasoline and the brake cleaner that I use (I recover them and reuse them until they are exhausted in the same bottle).Whenever I see a post from somebody using brake cleaner on their guns, I always think of "putting the cast iron skillet in the dish washer". Sure, you can do it, but why? It just makes your life more difficult.
You don't use to degrease your guns after spraying the oil to dissolve gunpowder residues and after first removing most of it with cotton rags? How do you clean areas that are not normally accessible? For example, have you ever seen how much crap keeps coming out of the firing pin channel if you spray inside it with the brake cleaner even after you thought you already had cleaned it perfectly. How do you degrease the inside of the barrel and the chamber after you have sprayed the oil that was used to dissolve the powder residues and after you have cleaned it with the brush?
I don't think oil is enough to clean a gun since the oil mixed with the dirt it has dissolved has to be removed. I assure you that the brake cleaner is also able to put out things that you would never have imagined were inside the recesses of your pistol, especially particles of unburned dust, specks of brass coming from the rubbing of the ramp against the case and other things.
In short, I am of the opinion that, before lubricating the weapon again after cleaning it, it must first be degreased and dried, otherwise you are lubricating where there is still dirty oil, I can guarantee it.
To degrease the gun I used to use the avio gasoline taken from its bottle but since someone recommended me to use the brake cleaner I have never looked back: much more practical and effective than the avio gasoline due to the powerful and precise jet. Then, it's not like it takes a gallon: just a few short sprays in the right places. Personally I also make sure to recover the liquid and use it to degrease other things.
I don't know which brake cleaner you are referring to to criticize the product and who uses it to clean guns. What I use is a normal C6-C7 hydrocarbon brake cleaner (avio gasoline is C6) that does not attack either the polymer of the pistols or the grips. Try it and you will never look back.