Tannins are only good for fish that thrive in acidic water. I run a blackwater tank for my South American pike and my Rhino Pleco because it's their natural habitat and they love having their PH around 6.6. I would recommend strongly against using any kind of drift wood if there are going to be African Cichlids in the tank or any other fish that likes hard or high PH water.
The drift wood will result in calcium being leached out of the water along with a drop in PH and the appearance of an Ammonia compound that shows up in the liquid test kits (the ammonia is from the wood breaking down).
As far as the wood itself, I got lots of larger pices and let them prop against the lip at the top of the tank when they float. There's a picture of my tank on my profile page if you're curious how that looks.