Anyone use  it?

I've tried this and took it off within a couple minutes. It takes away the 'weedless' advantage of a spinnerbait

Nope. As BaconStealer says, it's no longer weedless.

third on the "nope" camp.  I like the weedless aspect of it.  If hook up ratios is a concern try upping the size of the trailer hook.  I stick with 1/0's unless they are extremely nippy.

If we had more open water smallmouth spinnerbaiting opportunity here, I would.   A fried of mine, who is very good at that, does the treble trailer hook thing, and also uses a ball bearing swivel on that trailer hook too.

I have never tried it as my thoughts on it are a fish can shake or break loose a treble hook much eaiser than a heavy duty single hook. Especially one that swivels 180 degrees

Don't discount treble hooks as trailers on spinnerbaits or buzzbaits. I watched Gary Dobyns win an event on Shasta many years ago and the spots were slashing at his buzzbait. He added a large treble hook trailer and landed two critical fish as a result. If you fish smallmouth and burn a spinnerbait just under the surface and they slash at the bait, a large Gammi EWG treble will get you a few more fish on. Peppers makes an open water model with a treble as the primary hook. Options are a good thing.

I've tried them on spinnerbaits and buzzbaits, but I kept fouling the lure with weeds. There's really no need to compromise the weedlessness of your spinners; I find that a nice, 2/0 long-shank trailer hook catches plenty of extra fish.

For open water use especially with bait like a frozen sardine or greenie, it's referred to as a stinger rig, a nice set up for toothy critters, for bass in a vegetated area I'd pass on using it.

I have used a treble as a trailer hook on many occasions and had lots of success with it.  If you bury one of the hooks into your plastic trailer I think you;ll find the weedlessness is still there.  I typically will use them on swim jigs.  If I'm having trouble with the single hook and am in semi open water I will turn the single hook trailer upside down.  Definitely will pick up some misses with that one.

Superb trailer in open water. Not so much in weeds.