Bark busters are the kind that wrap around the bars completely and 'plugs into' the ends of the bars, correct. On lots of off-road riding, the course is routed through trees that are closer together than the bars are wide, meaning you're going to run into stuff occasionally to often. They're called bark busters because when you hit a tree, instead of your hands, levers, etc getting crushed, the bark of the tree gets busted and you keep going with fingers and components intact. That and I believe one of the original companies to make the things called them bark busters.
Either bent or straight works, comes down to personal preference. Some people like the idea of there not being a bar directly in the outside escape path for their hands in a crash, others (like me) don't care. The bent version will likely have more clearance for the stock levers, which I found to be a little long and in need of some trimming (or in my case, mud induced bending) to fit without rubbing on the guards.