They work, but buy non-inline unless you *have* to
They do work, but these inline couplers are a pain to work with if you are actually following CAT6 spec and are only leaving less than 1" of untwisted cable on each end.
Why? Because in order to clamp down the cable jacket onto this "inline" jack, it has to come in at a 90 degree angle to where the punchdowns are, which means you have to fight with it to get the individual wires to bend 90 degrees in a very short space.
This also means that there's no room for your punchdown tool between the clamp and the cable, so you run the risk of cutting off other parts of the cable when you punch down.
Plus, there's only a sliver of plastic on the outside of the punchdown space, so the cutting side of your punchdown usually just mashes the tiny piece of soft plastic that's supposed to work as the stop for the punchdown tool cutter. I ended up having to punchdown multiple times to get the wires snipped off. Note of you don't cut the wires at the termination you'll get more signal reflections.
In summary: These work, but buy the non "inline" couplers instead and save yourself a lot of pain.
Cheap, look nice when they work, beware they may fail
I had one of these fail on me, at the exact same time I did a bad flash on my router. So, of course I spent 3 hours trying to reconfigure things before I thought to test the connection with another device. I had one fail so I ordered 3 to replace itthis is one part which you should keep spares on hand!
PROS: Cheap, look nice when they work
CONS: They may fail... I know entropy affects all things, but... this failed much more quickly than I expected.