gives a good updated look at the sons of ether in revised, it's less annemic than the 1st ed SoE book and you get a really cool fiction story explaining the whole tradition in depth. it moves beyond the pulpy-paradigm of the 1st ed and shows how the etherites work as a complex organization, it takes them out of the realm of science-fiction and instead displays their real academic institutions and politics.

the only complaint is that this is kind of a halfway point between the older editions and m20, where the etherities in m20 have now become more inclusive and less gendered. this still treats female ether scientists like a small political faction instead of a huge part of the organization, so you should read m20 to understand how far the tradition has come since the days of victorian misogyny. other than that, this is a great sourcebook for players and storytellers.