After a discussion on Twitter, someone asked if there was a way to determine if the Skype for Business installation on your computer was MSI or C2R. The tricky part was that he needed to find this out without having a Microsoft Office installed on the computer. Had Office been installed, you could check if the Office Updates button was available. Update button = C2R.
I had Office C2R installed, and took a look trough menus in Office, Skype for Business client config and add/remove programs. No trace of C2R. So i opened regedit to have a deeper look. I at last found a path named like this that contained references to Skype for Business: Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\15.0\ClickToRun
Since it was Friday evening and i did not have anything better to do, i uninstalled Office and cleaned regedit for references to C2R. After a reboot there was nothing left in regedit. Then i downloaded the Skype for Business client and installed it. Now i could find the same regedit path i had previously when also Office was installed. So this confirms that if you see this regedit pathm you have C2R Skype for Business.
A quick way to check this without going trough regedit, is to run this command in PowerShell:
Test-Path -Path ‘HKLM:\SOFTWARE\Microsoft\Office\15.0\ClickToRun’