[JKT]

OmniGroup offers 24 hour trial licences for their apps so you can test out the full functionality of each. Easiest thing would be for you to test drive OmniGraffle for a while then OmniGraffle Pro for comparison. FWIW, I believe that the upgrade fee for OmniGraffle to OmniGraffle Pro is only the difference in the pricing of the two versions, so if you get OmniGraffle but find that you need (some of) the features of OmniGraffle Pro, you aren't losing any money so-to-speak.