Student requests to know their "grades so far"
If I were a student, I would prefer your second suggestion: A number along with some caveats.
Basically I would want to know what I have to do in order to pass.
When I taught my first class this summer I was giving my students a number and then a short note which explained that I wouldn't be assigning letter grades until the end of the course, so I don't know their letter grade along with a sentence or two about how I personally think they are doing and what I think they can do to improve. This seemed to work pretty well.