I'm a classical musician who has been reading old treatises on composition: Zarlino, Fux and so on. I got Morely's hoping for his slant on the topic but the printing in this edition is really tiny and the English is that of the 1500's. This makes it quite difficult for my 41 year old eyes to get much out of the book.
The Zarlino and Fux are actually much easier to understand because they have both been translated into modern English. Whereas its fun to read Morely's verbal style, his humor, I personally find the tiny print (it really could not be any smaller and still be sold!) to be very physically tiring -no, I don't need glasses, other books are fine. :)
Being familiar with British musical terminology is a must ("quavers", and so on).