The plating and engraving of the B&Os are quite nice.
The transformer is very small and the magnets are not terribly strong, so you have to be realistic in your expectations . Here is a picture of the insides of a perfect one.
Latest News from Crowley and Tripp's Lab: Duralumin in ribbon microphones
Note that the original ribbon is made of a type of high strength alloy. Over time it would stiffen and lower the output. Some people also say that alloy is prone to corrosion at the clamps. These mics have a sharp cutoff due to the parallel sides of the motor unit, and the surrounding ribs. I have a couple of them in the museum and people love the phallic rocketship look.