I did not have any experience with WAC LINEAR mini track products, but everything came together just fine. At first, it seemed like the connectors didn't quite fit (all of them, not just the jumper set), but with just some force, things slide together and nothing breaks. I bought everything as separates, so no instructions were sent and even WAC's website doesn't help with this LINEAR mini track line.
When pushing in connectors, it helps to have an end cap attached at the other end so you don't unintentionally push the copper? rods/rails out the other end. It's not a problem to slide the rods back in, but it's easy enough to have an end cap on there.