I find it interesting they are using a different lockup rather than their standard Purdey nose, hidden third fastener.
This is the "standard lockup" third fastner for Purdey double rifles and has been for a 100 years or so and not only them but the Holland is similar. The main thing to view is the increased depth of the action at the fences and more importantly the size of the bolster of the side of the action to attempt to prevent the action from moving away from the barrels during firing of the cartridge. Also on a double rifle the draw of the action lumps is in full tight contact with the corresponding circle of the action to hold the barrels tight against the face of the action. Holland and others now use a replaceable draw insert that helps reduce the time of fitting the draw to the circle and of course the replacement for eventual wear. If you want to know about all this then read Vic Venters book GUN CRAFT chapter II --Jointing and the Circle. Vic's book should be in every double gun enthusiast library.
The Westley Richards dolls head third fastner and the Scott screw grip third fastner are better methods for double rifle and have proven so during the more than 100 years they have been in use. But alas there are only about 2-3 double rifle action makers in the world who can action a WR double rifle, Mark Mitchell being one of them.