My OWB (CB 5648) will burn just about anything - wet, green, punky, wood if necessary; shovels of bark chips; paper and cardboard; big stuff, little stuff - it eats it all. However, I try very hard to feed it clean, dry, split, well seasoned wood. The same wood you'd feed a gasifier. My business partner installed an EKO 40 in his house and he has a 1000 gallon insulated tank in his basement. He can run 24-36 hours in the winter, might even be a week in the summer with solar backup. He can't burn any of the junk I can. The nice thing about the OWB is that I have a pile of stuff I wouldn't feed an indoor woodstove or gasifier, and about once a week I'll try to get a big bed of hot coals going and toss some of that punky, gnarly, knotty junk in there with some smaller sticks and it will burn right up.
Also, if the OWB is fed properly, it will not emit much smoke at all. Almost nothing visible toward the high end of a burn cycle, and just thin wisps of smoke, probably more steam than smoke, when it's shut down.