I don't know how robust they are. I understand your doubts, but it seems to me that, if they would make your life more pleasant and rewarding in your hobby hours, all it would take is a quick meter check for continuity before moving on to another wire and joiner combo at the next joint. Place one, connect to the bus with a wrap-around bared end, turn on power, and see if you have voltage there. Or even better, do an ohm test with just the terminal joiner on the bench to see if their solder work is holding up and if the wire hasn't broken inside the insulation.
They must have a market that keeps purchasing them and keeps them in inventory. So...............someone is buying them in quantities that mean they're constantly available. They must offer a solution of some kind to some people, and it could be for you. I hope they do.