I must admit for starters that I have not tried the freePBX contrib, but I am using the SAIL set up, everything to do with asterisks can be complicated and it has taken quite a while for me to get things going the way I want it, and the support from the Sark devs is good here in the fourm's plus regular updates to the SAIL rpm also.
I will try the FreePBX system sometime but for the moment I will be sticking with SAIL.
I'm not sure if FreePBX can do the Multi-tenant, this is another reason I stuck with SAIL, anybody know if FreePBX can do Multi-tenant ?