I believe the reason they say not to use POLYGON on moving objects is because entity models are usually complex shapes. A model will use its real polygons for collision with the POLYGON flag, and could get stuck and cause many more calculations on the part of the movement function.

That's why I used the box model for collision, its not complex and it works well. I haven't had any performance issues or collision anomalies. It seems to work better than the OBB in everything that I have tried.