Well, if you are using a boring head to turn the outside diameter of a part, you'd need to use a left hand boring bar. If you are boring out an internal hole, you'd need a right hand boring bar. There are some boring heads that can also do facing of the end of a part but this product is not that kind.

I'd say it's unusual to use a boring head to turn an external diameter, which is why I think you will usually find that the boring bars supplied or recommended are right hand. I would tend to use a milling cutter for external surfaces, rather than a boring head, especially if you have a CNC milling machine, or using a rotary table if you only have a manual milling machine.

Boring heads have only a single point cutter, so they are very slow means of removing material. And they aren't very rigid, so are not suited to heavy cuts. The main reason for using a boring head is when the finished surface needs to be a precise cylindrical surface eg for a bearing or an engine cylinder bore.