Basically it is the same tool, however scope of available tools and features depends on status on Server Suite (IGC.Premium / IGC.Premium Plus) subscription.
Every Customer having active subscription of server license is being automatically set to IGC license type of ToolKit (Premium), where Customers not having active subscription, or server license at all, are being turn into MU license type of the tool.
What is IGC.ToolKit?
The IGC license of the tool is fully featured and not limited (with exception of available tool plugins) version with all available editors and export options to support IGC Server files.
What is MU.ToolKit?
The MU license of the tool is version that do not offer editors and export options that are unique or exclusively used only for purpose of IGC Server files.
Switching between IGC and MU ToolKit (Premium) is automated, dependent from server license subscription status, however may require tool restart to apply the change.