I have US made Coppers, and Brass, very little difference in how they age. the inside of all of my Copper and brass usually remains fairly clean unless soiled in some way. I'm no expert metallurgist, nor am I all that well versed on the different grades/types of metal, but as far as I know the only lead free brass is Naval. As for the copper who knows what is in any of them.
Not all that long ago there was some debate as to where SOI was having mods made, rumor was the same China shop Kindbright used for the SOI clones, that was one reason for SOI's major butthurt over the clones. I could see no difference in the SOI shorty I had and the Kindbright, every single part would interchange, and they even formed the same color patina. Most larger cloners in China have authentic pieces sent to them for copying, typically the better makers are extremely close, sometimes even better. The Skyline RTA is prime example of this.
I'm also not concerned with the prospect of slight lead content of non-naval brass or Chinese copper. Atomizers, yes, mods no. But that is a personal choice, and neither right or wrong. Now maybe it is on a personal chemical matter But none of my copper or brass has ever discolored my skin, nor does it smell like a dirty penny. If it were a concern and I didn't trust the metallic make up of something I'd just slap a chemically inert clear coat on it.
The SRZ is a good clone, I've had no issues with it at all, when they arrive TYD the brass and copper will be clear coated first thing I do with pretty much anything I receive is strip the CC off if it has one.
I guess bottom line is if your concerned with what its made of avoid it.