Very interesting Barry, and good looking collection - have to admit I've succumbed to collecting the odd one or two. These things pop up in the most odd place - often with Sellers not knowing what they are.
We've had one or two relevant posts on the Board in recent times - which you'll find if you use the Board's search facility - although they seem to have a limited fan club.
Literature is rather meagre - there's Stephen Parry (1981) or Brian Brooks (2000)? I can't speak of the Parry volume, and Brook's offering is really only a 33 page booklet - by very interesting and worth having if you can find a copy - most other books - for example Hajdamach - tend to have the odd page only.
Most do seem to be either Scottish or English - shows what a bunch of 'lushes' we are in the U.K. I guess - but like you I think they are very interesting pieces of real history - and some go back as far as c. 1800. Some of the notch indicators can be difficult to see unless you know what to look for, and the lead seal marks need detective work to interpret.
Somewhere on the Board we have a link that gives the identification of these details - if I can find it I'll post the link. Bit busy today.
Ref. 'Miniature Decanters and Whisky Measures' - Stephen Parry - 1981
'Whisky Dispensers and Mesures' - Brian Brooks - 2000.