It looks like mopani wood to me as well and I had a bunch of it in my 55 gallon. When you put it in did it leave the water slightly stained for quite a while? It lessons after a while as it leaches out but is quite evident at first. As you mentioned also it is usually quite dense and has more round edges and is more branch like than a straighter lighter piece of driftwood. Mopani wood is good for that as it puts out natural tannins (dark circles in water, specifically desired by brackish fish) which coincidentally a betta would love.
Very nice setup. I am jealous though it is probably the size (or I just have a really cranky betta who doesn't want to share his house) but my Cerulean did not tolerate his tank mates. He is on a 2.5g and I got him a ghost shrimp and a golden snail. Well the shrimp was in 3 pieces, one of which was his head in the morning (so gross) and the snail was tortured continuously for about week and knocked around so much he was never able to come out of his shell and one day just never came out again.
so the conclusion was he likes being a bachelor. I am not sure about my other boy Calypso and whether I should even bother trying, I think the tank is too small and they get very attached to all of it and especially the hiding places in the logs and under stuff where shrimp also like to hide. Thoughts?