I have not replaced the brakes on the PP yet (inspected, cleaned and repacked each year) as the shoes & magnet are still good. I do have several other trailers and replace at least one of them each year. I always replace the entire assembly (backing plate, shoes, magnet and hardware) as it is much easier (requires cutting and re-connecting the lead wires and removing/re-installing 2 to 3 bolts) and usually cost the same or less than ala carte pieces. I normally pay around $140 for a pair of assemblies.
Daniel & Donna Leonard
2011 Ram 4500 SLT 4x4