Without having tested dropdowns myself, I would say that they are well-known GUI elements, and probably very usable. I like that your design is compact - its easy to get an overview as a user.
But if you worry about usability in the context shown, maybe add some micro-copy (text which explains what the element does) near the dropdown and test that?
As shown, I find the GUI hard to understand. It would hopefully be easier in context, but I still think there’s room for improvement. Consider micro-copy next to each group of elements, as well as placeholder text in those form fields to the right (and why not in the dropdown?).
I guess users will learn the interface eventually, but you still might want to reduce the risk of user errors due to confusion or cognitive overload.
Just my humble opinion - maybe some GUI-ninja can chime in too?