The ease of use, it's flexibility in terms of what can be flown with ground control software for different platforms, including drones from PhantomWorks/DJI and others which are not compatible at all without some additional plugins or workarounds.
It also has great customer service if there ever was any problem during my testing period. I have been working as part of team to help launch their API program. This helped our business immensely by providing us access to thousands more customers who otherwise would never consider buying our product but now do because they saw we were able to integrate them into GCS system so seamlessly!