Brake cleaner and Gun Scrubber are essntially the same thing as far as I am aware; that is except for price. While Gun Scrubber warns against using on certain plastics and polymers, I have yet to see it damage any guns made with such. I am not saying it does not happen, i think the previous poster can attest that it does happen, I am just saying I have never sen it. Then again I only use it on newer guns. I have used it on Glocks, Remington 870s and HK MP5's. It gets that MP5 really clean, really easily. It smells though, like a quick trip to the morgue. I recommend using it with excellent ventilation and maybe a protective respirator used for sprays and mists if you use it a lot. One thing about it, if you clean a Glock with it for the first time, you may get really worried when the finish of the metal turns powdery gray looking. Nothing to worry about, just a drop or two of oil rubbed in a bit and it looks as good as new again.
As for carbeurator cleaner, I was always told to stay away from it for use on guns. I have never used it on a gun but, I remember using it on some cars. Another: smelly, horrible & irritating thing.
Best regards,
Glenn b