I think we are all well aware of the problems
@Buckeye Amps and
@Rick Sykora found and fixed. That is a well-understood issue. My concern about the marketing ETI espouses has nothing to do with that, and I do not see how the previous issue is relevant to ETI's marketing (etc.) Here is an excerpt from ETI:
Brass has worse conductivity than copper, true, but in the real world there is little difference. Gold also has worse conductivity than copper, for that matter. Nickel is slightly lower than brass, but is much harder, and that is the reason many manufacturers (of many products, like my trumpet) plate with nickel before gold. Copper is soft and nickel provides a hard surface that better resists wear and can help maintain a solid gold plating. Since they gold plate over the copper, or nickel, I question just how much a Ni plate under gold degrades the audio signal.
As for the housing, aluminum is light and has high strength-to-weight ratio, but is weaker than other materials (like steel) for equivalent thickness. Aluminum is nonmagnetic which is helpful in some applications as a shield, but since the housing is not connected to anything (not grounded) it's shielding properties for the length of a binding post are negligible. Especially compared to the much longer runs of (typically) unshielded speaker cable.
I like the idea of high-quality binding posts, and ETI is probably as good as any mechanically, but would like to see proof of their claims especially with respect to audibility.
To put some numbers on it, using 0.25" diameter posts 1" long to approximate a binding post (assuming pure material for the entire post):
View attachment 323433
So yes, brass is less conductive than copper, and nickel is significantly worse than brass, but the nickel layer is a thin plate (and gold even thinner) so the effective difference is smaller than the pure resistances in the table. And note the resistance of the speaker wires far dominates (by several orders of magnitude) the overall wiring resistance of the system.