Clear mission. Very stable on every platform (even with huge multimedia sets and videos in a graph). Mobile friendly. I guess some small design improvements needed but overall: decent experience.
+ I love something other visual (and especially „mind-mapping”) tools omit: presentation layer. You can present not just your whole graph as it is (which can be confusing for others – where to start? what next?) – **but you can share suggested path through you knowledge only.** The presentation mode is a killer feature.