Many of the kits are “made” or compiled by just few suppliers. So they are built or made to a price point........sold to many different venders.

Some are complete are actually designed to work together...........like master cylinder and portioning valve.

Many kits recommended replacing the ball bearings with tapered roller bearings. Replacing the hubs is great option and often cheaper than just the bearing when purchased in a complete kit.

I would replace all the brake lines during the install.