pretty good
Heavy going, some of the time, and quite often words are used in exercises or
examples before they have appeared in vocabularies. The coverage is
systematic and thorough - e.g. a list of all the inflective adjectives
is given at one point. I recommend the book for someone who already
knows some Swahili. For the complete novice Steere's Swahili Exercises
is probably better. Ashton covers the verb well, and intersperses stuff
about nouns, and for a grammar of Swahili that is the right approach.
Be warned: the language is not easy for a native English speaker,
vocabulary as well as grammar being strange to us.