Sorry for the delay in response,
It seems that Guest is fairly straight forward and a significant improvement over the existing controller based guest Captive Portal
OnGuard's functionality appears diverse of any of the other modules.
It appears that QuickConnect may provide some of the same functionality that Onboard does but is cloud based not requiring the ClearPass Policy Manager?
The Profile module seems to duplicate some of the Policy mananger functionality. These are only my perceptions based on the available documentation in an effort to evaluate them for purchase.