I use my steamer weekly on my old-style Avian Adventures cages (12 years old), as well as several newer models of Kings' cages and never has it knocked any of the powder-coating off any cage. I think you can steam with confidence that your cage will be just fine.
I have a steamer and will never go back. An hour long process turned into 20 minutes, plus the cages are far cleaner because it reaches the incredibly difficult places to clean/disinfect. I love it.
Presently have six Greenwing Macaw (17 yo), Red Fronted Macaw (12 yo), Red Lored Amazon (17 y.o.), Lilac Crowned Amazon (about 43 y.o.) and a Congo African Grey (11 y.o.)
Panama Amazon (1 Y.O.)
I consider those essential cage cleaning tools, and I echo the remarks about getting to the really hard to reach places, and just melting and wiping...
Definitely a useful cleaning tool. Well worth the hundred bucks or so that they cost.
I use my steamer weekly on Dexter's cage. For some reason he loves to stand on his perch (away from the cage, obviously) and yell at me the entire time I'm half inside his cage, crouched in crazy positions steam cleaning. My husband says he's telling me not to miss any spots.