Those locking plugs used to be found at many audio sites like PartsExpress (they no longer have them). I was using them prior to Bluejeans offering them. My older GRs used unusual binding posts which were split and I found that if I tightened the locks and they were in the wrong orientation, it would result in a snapped tip. So I stopped using them on the speaker side, but I still use them on the amp side.
I agree that Bluejeans is not exactly "inexpensive" but I would say their price is absolutely reasonable for the quality AND service you get. Yes, you can get less expensive cables and such, but you are not going to get the same quality for your savings. Their price is still lower, in many cases significantly lower, than most boutique cables that offer no benefit at all over what you'd get from Bluejeans. For my third system, I didn't use Bluejeans actually. I went with some cheaper stuff because I didn't feel I needed that level of quality for a simple setup and it works just fine.