[JKT]

I should have pointed out - you can get as many 24 hour licences as you want (within reason) so long as there is a pre-determined period between each (48 hours I think).

FWIW and for the benefit of anyone else reading this thread in the future with a similar query, as someone who only uses the Pro version it is a little difficult to know which of the Pro only features I do use a lot aren't in the basic version so giving you a valid and objective response to your original question would be difficult. My implication was that you get the basic version of OmniGraffle and then, once you get used to the app, try a day licence for the Pro version to see if you did need or want the additional Pro features or not.