In my experience with firewood slabs will not burn very well. There is no room for air between flat slabs so it can not breath and burn well. Circles mixed with triangles is the best but most people want every stick split. Huh go figure but with triangles it is much easier to get space between them than flat slabs for it to breath and burn good. But if the slabs were thick enough you could split them into triangles. For me they have to be oak or people in town will not buy. Huh again there are lots of good burning woods but if you try to explain the types to people in town they still will not buy. Must of had a bad experience or something..