There's not a "demo" of MindNode Pro but there is a "lite" version. It's free at App store (also maybe free at website). MindNode Pro has extra features (naturally) and I definitely think they are important enought to pay for the full pro version.
Here's a link to a comparison chart (PDF):
https://mindnode.com/support/FeatureChart.pdf
Here's the link to their website:
https://mindnode.com