WHMCS is severely bloated, has programming logic littered all around the templates, is ENCRYPTED with ioncube, and is generally difficult to customize professionally. its almost unheard of in the web-ware world that you pay for software and are unable to alter the source.
all of these things are very bad news if you want to do any heavy customization in the future, make the package look more professional, or upgrade easily. money isnt a problem for me in this particular project, so i bought a license and have been developing on it the last 6 months. very regrettable; WHMCS out of the box has a horrible, convoluted UI and streamlining it to bring the standard up is not a trivial process.
that said, development is fairly active and bugs get fixed quickly.
more people using genuinely open source like phpcoin is a very good thing. free or not.