Hey, i have one of those exide hones too!
Have you done any experimenting with it? I'm going to try it wet and with lather eventually, but probably not for a few weeks. I've got two stones coming on loan to play with in the immediate future.
Only barber hone I have in my possession.
With the exception of maybe one or two, they all look like they are rather inconsistent in their abrasion and do some damage as well as refinement. The nox looks like it straight up murdered the edge. I'd be really curious to see if the edges have this quality under magnification from something freshly made out of the oven. I still really think they had to have been better new. Like an old car that has had some hp escape from the block.
Ian have you tried one of these unmarked synthetic stones? I guess it could be considered a B hone?