In order to repair these do I need to use primer and paint?

I am in the middle of repairing these cracks. As you can see I have worked on the two on the sides, but I am not really happy with the result I am getting so far. I used 3M fiber enhanced compound as it seemed to be the most rookie-friendly product I could find. But it is kind of hard to sand down. And I am not sure it is the best thing for crack repairs, so I haven't applied it on the middle crack, which also happens to be the largest one. I just stuck a length of mesh tape on there.

I'd like to avoid repainting the wall if possible. So my questions are: should I change to a better compound for the middle crack? Anything I should pay attention to? Do I need to use primer and paint after compound or is there a way I can avoid repainting while still get a fairly uniform and consistent result?