CloudMonitor can work in 2 different modes. The most basic functionality requires a Service Principal with Reader at the Tenancy Level.
For more advanced functionality, such as letting CloudMonitor implement the cost-saving suggestions for you, Contributor is required, however, this is completely optional. Why not try the free version first in Read-Only mode?
No 3rd party or Guest accounts need to be created for CloudMonitor to work. Please ask your IT Team to contact us if they have any concerns so we can have a chat about the security controls in place for CloudMonitor.