WHMCS (I Use It As A Host, And I Am A Client Of A Host Who Runs It)
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Functionality
Amazing, dozens of features and they keep adding more in every update, it has a built in affiliate system and support system.
Customer Experience
All my customers along with me seem to like it as it is easy to navigate and find out what you are looking for.
Integration
Integration is simple, all you have to do is really edit 2 files header and footer and your good to go!
Bugs/Faults
It can be hard to navigate admin panel as an administrator if you are looking for the support area at times.
Ease of use
Extremely ease to find everything as a client and administrator, its all layed out well.
ClientExec (As a client)
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Not a big fan, hard to navigate, poorly designed, poor functionality.