Although there is some overlap with Machinery's Handbook, Newnes Engineers Reference et al Kempe's is a slightly different animal. Besides some data tables it has numerous short articles on a wide range of Engineering and "real", as in doing something practical not modern make it pretty, Design related subjects.
I'm inclined to think it intended more of an aid memoir for designers who have not really looked into a subject since university or HNC courses and a quick primer for project management folk who need to either produce sensible outline specifications or verify what they have been given on a quote makes sense. If, like me, you learned to read out of the family encyclopaedia you can read the articles as either an interesting primer or something to get your tried on a new topic. In my working days I found it very useful when les bosses assumed they could pull a fast on on a subject I appeared to know nothing about and as a starter for 10 when I had to dig out some rather specific information in an unrelated field.
Realistically nowadays its for the guy who likes books rather than a live information source.
I have the 1985 and 1996 editions.
Clive.