We have two books, an orange one and a blue one, and they differ subtly - Ritz plays a tenor uke with re-entrant baritone tuning. The orange book has the fingerings for this uke (labelled as "tenor") under the musical stave, and the fingerings for soprano above, resulting in the same chords each time (with variations dictated by the different position on the fretboard). The blue book has one set of fingerings for all ukes, no matter what the size, hence the music is in two different keys. In the case of the blue book, then, you may find the stretches to be just too big if you are playing a tenor or bari and your hands are small.
Whatever way you look at it, these books require (and repay) genuine good old practice! They have much more content than you may think - 25 songs is a lot - if you practise each song for a week, it will take you 6 months to get through one book! The arrangements are gorgeous, and the books are superb for someone who has just begun learning harmony and jazz theory. They deserve more than 5 stars*.
*although there are some small problems: one or two printer's errors can confuse, and also a lot of chords are labelled as Major 7 when I suspect they should be labelled as Major 9 (e.g. 0202 is labelled CM7 on soprano, which makes no sense, and anyway the bari is clearly not playing a major 7 chord, whereas 0202 could have been a misprint for 0002. Labelling 0202 as CM9 makes a lot more sense and it ties in with what is going on on the bari, and later on we see genuine examples of M9 chords, so that we know Ritz definitely makes use of them)