There's a lot to be said for a 2" (~50mm) boring head. Short extension, can use 1/2" shank tools for smaller holes, can bore larger holes with bar out the side, etc. Any of the cheap ones work fine, some are harder to read than others. I'm not sure how often you would need to reverse a boring head on a mill. I do it sometimes, usually when using a boring tool to turn a boss. Using the inside tool to cut an OD makes the geometry "reverse" and hence the rotation needs to be too. Beyond that, most tools are going to be RH anyway unless you make them for yourself.
But unless you only do small stuff, you might eventually like a range of boring heads up to about 3" for the BP.
The primary difference between a "good head" and mediocre ones are 1.) the ease of reading an accurate dial, 2.) the ease of adjusting combined with a smooth action that will repeat/always move the same for the same dial increment. Criterion heads are a common simple head in the USA that are very good at this.
I agree with John that BP's own head is a pretty nice one. Relatively huge dial (easy to read, easy to adjust) for the size head, one piece head and rugged. The 5/8" bar size is kind of unique, most are either 1/2" or 3/4" (or larger). 5/8" is kind of intermediate and if you do work in the range, it is a convenient size though possibly the bars are less commonly available. They don't have much offset, but that does not have to be a hindrance; move the bar out to the outer hole or stick it out the side instead of using a large unbalanced offset. Mine's beat to heck by the previous factory, but good tool to have on hand. I sold a Criterian to keep this one, but in fact often just reach for the cheap chinese 2" unit when a small bar size is needed.
Wohlhaupters are nice. Less convenient for routine moderate tolerance holes. But when you want to dial them in a few tenths at a time, it is easy. Includes facing capability. UPA3 size (~3") is about right for a BP
A bit esoteric these days, but if you want to bore tapered holes or bosses, a Tree boring head will do the job. Most are also "tenths setting" with the ring, for straight up and down boring work. Of course with the angle slide, even the non-tenths units can be set to dial "tenths" based on the sine principle. A bit ponderous of a tool for routine boring, though. Also don't take "normal" bars. You have to grind tool bits to fit the proprietary set of 3 bars that come with every Tree unit.
Just to confuse the issues.
smt