For the benefits of us who are not sure what is the meaning of
two pieces blade or
sandwich blade or whatever you call it, I took the liberty to show a close up of such a blade which I spared and opened the welding (It was easier than easy).
And fully opened:
I have never been to Yemen and never seen how it is being done (I wish I could but due to certain political obstacles I can not do it). But in my very humble opinion, at least the blade shown above is of very poor quality. It is made of two thin, 0.5 mm thick, galvanized iron sheet pressed in a die (see Lew comment above) and badly welded (not soldered), which make the task of splitting it open very easy. In my very humble opinion, the round rib or the squared rib is only a question of who pressed the blade on what die.
I am afraid we can not regard it as a weapon or a tool and only hardly accept it as a traditional costume artifact.