The disadvantages:
1) They would probably melt after anything more than parade-lap track-use...or a run down the Dragon/your favorite Canyon.
2) You keep having to explain why you have fake plastic brembo covers on your brakes at car shows.
before you do any "mod" to your car, think for a second, "will I have to make excuses for this"...if the answer is YES, it is probably a bad idea.
Back on topic, I used some Parts-Chain high-temp paint to do some calipers on a friend's 240sx project (silver caliper, w/red lettering now). ~2 years later with street & autocross use and they still look great from 5-10ft away. Up close they are starting to chip a bit, but considering the process averaged to about $2.50/corner...pretty good value.
The reman calipers on the front of my NSX came silver, but turned immediately rust colored as soon as they got some wheel cleaner on them mixed with brake dust. Not sure what kind of paint that was, but I'm going to re-spray them over the winter. Probably either silver or black.