I didn't know about those connectors when I purchased these, but I saw them yesterday when I was looking them up. Cool! Good to know for the future. Soldering it wasn't too hard, but I did mess up a 3-LED section or two on failed attempts.
Regarding your failure predictions, I am afraid you're right. So far, on the steprail, I have one 3-LED section out. I can't see any physical fault, but if I press on it a certain way it will light back up. Just a broken connection on the super thin PCB I think. In the interior, I have one 3-LED section of red out because I accidentally clipped it when putting my seat back in! Same deal with that one, I can push it a certain way and it will come back on. I am not too worried about these failures right now, but I do hope they don't continue to fail.
Seconding your recommendation about DONT TOUCH THE STICKY!! It's not very strong and I wouldn't recommend it for outside use, it will fail eventually. I ended up using RTV to hold the steprail lights on.