I have the AoE 3 hardcopy - but the Kindle edition is on sale as well.
And before you scream at me Kindle is crap for textbooks - it is the Expanded Layout edition ("Print Replica") - that won't read on a normal kindle - but only on PC's, Tablets & Phones.
Version on Kindle is 7th printing of 2016 with corrections.
So a very nice "portable edition" for GBP 23,- with full text search. Content Index pages are not linked to destination pages it seems.
But there is pop-out index
I would say it is worth every dime.
- I know one could probably find it on the internet in PDF format. But I do like paying for things I like and use.