I've used it.. and honestly.. after the eventual decision of the XF staff to actually interact with their license holders (after much poop being thrown).. I
renewed my XF expired license. That site is a "play" site for me currently as the current style is the default that I'm having fun tweaking.
I may renew my IPS license to play with it on another domain (I like to be able to keep somewhat up to date)... but what keeps me currently on XF is not their base script... it's the 3rd party developers that they are so dependent upon. The dependence on 3rd party developers in many aspects does not give the "price point benefit" to XenForo...But it is what I am comfortable with, and have used on a site since 2012. But many of those 3rd party developers offer products that far exceed what you can get on the other competitive paid scripts.