I had success and like them!
We use a couple 4 shooters and I have bird baskets for one.
I used a stake in front of the machine to attache the lines to, and used them with both dead and live pigeons.
For walk ups, some upland work, and for putting live pigeons out on marks I like them a lot, especially nice when we have more than one dog to use.
They are a bit labour intensive and a baskt that had a bottom and mesh instead of just the strap would faciliate a faster way to load the live pigeons...
I couldn't say what we were getting for height on dead birds, but on live birds that get even a short flight off the launch the dogs got good marks and success.
Setting up the lines correctly is all important and on a few instances line tangles chopped the launch short - which sucked.
There are times where I will continue to them.