Brass doesn't scratch glass, thats why they were all originally made that way. The introduction of the stainless came about because they needed a cheaper lightweight non-rust channel. The glass was forgotten about.
Sörbo were the first to really come out with an alloy aluminium that was lightweight for its superior size. Personally I still reckon the Sörbo has the edge on bigger channels to work with, especially for high pole-ing. I tend to go for a lightweight Pulex or anything to hand really for up front working. I have them all. Sörbo still make the best rubber, probably out-lasting any other brand 10 to one. I have had some bad batch of all the other rubbers, but never good ole Sörbo. You can recut them to make a new edge, but its too faffy for me, thats the idea of the cutting machine they sell & the different grooves in the Sörbo channel. So if you were to cut them 3 times & taking into account the 2 sides - you would have 30 times longer use. I thonk the price of the docket has come down now, I may rethink buying it with all the dodgy rubber I've had!