One other catch is that while your ticket is unrestricted, the free companion ticket comes out of a limited availability bucket. I almost think it is the award bucket but am not sure. This means your companion will not earn any frequent flyer miles and if it is peak season you may not be able to fly on the days you want due to the restricted availability of the companion ticket.

Also, if you want to use this for BA, be forewarned that they did not renew with AMEX so as of right now they are not a part of the program anymore.