I booked a flight yesterday after activating the $600/$150 offer on my Platinum Charge and got the email saying I'd used my offer shortly after the order went through. I received my $450 travel credit this morning and will see if the $150 comes through or not.It should be stackable, but until someone tries it out, we won't know for sure. So in theory with the $600/$150 offer and the $450 charge credit you could book a $600 hotel and get $600 back if it stacks.