I like that it has all of my endpoints, so when I make changes to one service, they're reflected everywhere else! It's pretty easy to use once you get used to how everything works with the toolkit.
The UI could be more user-friendly - not everyone is familiarized with using APIs or REST services yet. There were some times where we couldn't figure out what was going wrong until someone pointed us toward documentation/support forums for help. We've been able to test our backend applications without having to worry about breaking them by testing against live data sources since this allows me to have confidence before deployment.