I didn't buy a kit. I just bought the rotors and the calipers (with brackets) separately.
For the calipers what I mainly need to know is if your original units are post mount (PM) or International Standard (IS) where they mount to the frame. Most budget bikes use IS mounts, but there are always exceptions. Once you know that, buying the right brackets is easy. This is why I need a picture of where they mount to the bike.