For BW printing on multigrade papers you need to adjust the 3 color filters to achieve the various contrast grades, so in the case of this head, it has three dials on the bottom to adjust the combination of the three, mostly the yellow and magenta. You can open the head and make sure those filters move back and forth freely before you buy it. And make sure the filter glass itself isn’t broken. I found it easier to just use a below the lens filter system. It’s cheap and easy to use. The settings of those filters built into the head can vary slightly depending on the paper, so I have read. I think lots of people do use the built in filters though..
The bulb isn’t hard to find assuming it needs one.