Magnetic brake lights

I got ours from O'reilly Auto Parts. HD wiring and magnets

Harbor freight, under $20. some folks have said they were wired backwards so be sure to check that out.
bumpy

Ones from Harbor freight do work if wired correctly. My set needed rewired. Still have them but hardwired into existing so they are not used.
These are good!
Magnetic lights

I think I can safely say NOT Harbor Fright. At least the entry level ones with regular Stop/Tail bulbs in them. Reasons:

1. The wiring is so skimpy they don't illuminate properly. An LED version should be OK in that regard because their draw is so much lower. BUT...

2. The magnets didn't hold very well. Admittedly I had them up in the moving air, but I lost one on the first trip using them.

I have a lot of HF stuff, but the lights didn't show me much. That said, they have Magnetic LED on sale right now $30/set. They'd probably be OK stuck to a flat step bumper, behind a tailgate. Not sure they'd stay on rough road/and/or windy day.