That looks much better then knotting! This saddle doesn't have holes along it though...it had 3 handmade holes in one section and it doesn't have a keeper. The keeper must be the tag with a slot in it? I'm pretty sure it didn't have one of those.
How does the latigo running up through the keeper differ from an off billet strap then? Well, besides length.
The latigo buckled using the tongue on the cinch then ran through the keeper is different because by looping the latigo through the cinch twice and having the tail it give a little more leverage to make it tight as need be. But, in my opinion, that is the problem with using the buckle tongue is that one hole may be too tight and the next not tight enough. On an english girth/cinch(correct me if I am wrong) they use buckles but there are elastic bands that help with the proper tightness and adjustment making the difference between two holes either too tight or not tight enough easier to deal with.