All code/listing issues aside it is clear these were designed for connecting 2 sections of a manufactured building together, not simply splicing or tapping a circuit. They are made with 2 parts that mate together, plug and socket fashion, after the cable connection is made up. I imagine after they were placed on the market someone said "say there seems to be a loophole we can exploit to sell more of these". They made the rounds about 10 years ago and I even had AMP send me some samples. Most of the folks I was yacking with at that time said this was only for manufactured housing but the code didn't address it specifically enough. Most inspectors hated them, hence they got far from universal "approval" and the issue went away. None of the guys at the IAEI meeting who saw the ones I had said they would take them fished in a regular wall.
The last time I looked, maybe a year ago, AMP, (now Tyco) was only addressing the manufactured homes in their docs. I see it is back.
