The OP should book through a Preferred Partner. Unless one already had contacts with the hotel (which sounds like it may not be the case) there’s no question that FSPP is the best and easiest way to get value added. And they can get value add IN ADDITION to virtually any published promotional offer on Four Seasons’ website.
Four Seaosns in particular has very strong ties with its top travel agencies, who are part of their business model. So, it can only help to book through a Preferred Partner, there is no downside.