Between Planets is always an odd duck for me amongst the Heinlein juveniles. I recall it being one of the last ones I read, partly because the opening with the ranch was so far outside what interested me.
Once you get past that it is of course a fabulously fun read with some political insights that I wish were in wider circulation. Specifically the tactics of the Venus Republic show a clear understanding of history: warfare against your enemie's civilians fails. All it ever achieves is to piss off said civilians, thereby boosting their loyalty to their current regime.
Equally, brutality against your own civilians is also ultimately stupid and the main character Don Harvey learns this through experience.
The politics is mostly shown rather than told (although there are a few digressions about Commodore Higgins that almost veer into lecture space).
The final episode of the novel (the mission to Mars) is much more a part of the core story rather than the tacked on episodes seen in The Rolling Stones or Farmer in the Sky. Having said that there is a natural break point in there that is probably due to the serialisation of most of the juveniles (as baby_elvis pointed out re Farmer in the Sky).