Not really a full review, but it's probably a little unfair to judge an ink that's older than me too closely on it's current performance.
Stephens' were founded in the early 19th Century but effectively disappeared in the 1980s, although I think the brand name was bought out. Once one of the best known British Ink manufacturers. Stephens' blue-black was used to sign the Treaty of Versailles.
This bottle is priced 71/2 d so definitely dates from prior to 1971 when decimalization came in, but I can't date it in any better than that. Effectively this is an ink that's around 50yrs old. Obviously I had to ink up a pen (Namisu Orion with Bock xf nib):
I used it undiluted, as it doesn't appear to show evaporation issues.
It's very quick drying - around 10 seconds and highly water resistant when dry.
It looks very blue in the bottle, writes more like a dark blurple when wet, but the purple element changes to dark grey as it dries, leaving a true blue-black.
Not an exciting colour, but a well behaved ink that showed next to no feathering or bleed through even on cheap paper.
Not the most lubricated ink I've written with (although not terrible), and writes slightly on the dry side.
It was still commonly found in Stationers in the 1970s so I suspect other part used bottles could be found with limited effort.