I made a king size bed frame and chose the combination of a solid tenon and a connector. Two years later, it’s still rock solid.
I chose the solid tenon and connector because the solid tenon eliminates any twisting of the joint. I found I had to be extremely precise in cutting the mortises and even practiced using scrap of the same dimensions as the bed frame.
I assume you are using the 700 connectors and not the 500 connectors.