the compass would point towards the poles on the dual earth model, because that is where the magetic field exists.
Umm no, that's incorrect, the compass needle lines up with the magnetic field lines, it just happens the field lines on earth run mostly north/south, in a dual earth model the field lines are vertical not horizontal.
Ergo, the dual earth fails to explain what we observe with a $1 compass.
The flat earth disk magnet model with south pole all around the outside edge is a nice try, except that fails when we notice the south magnetic pole is a single location, so the disk magnet theory collapses, thus the flat earth model collapses, since a flat earth can't have two poles.
Maybe you can clarify the dual earth model by showing what you think is the magnetic field diagram
Just a follow up on magnetic inclination, I found out that some good quality compasses come pre-balanced to cancel the inclination, some companies sell them in different version depending on the region where you live. There are also some compass manufactures that have come up with global balancing schemes to cancel inclination
http://www.recta.ch/en/declination-and-inclination