These are special mouthpieces intended kids starter instruments.
They don't fit standard instruments.
I bought them alone to be cheap mouthpieces to try out with cardboard instruments. I'd always wanted a brass mouthpiece (but they are usually pricey) and I'd been curious about flute, so adding cones or tubes to these mouthpieces makes interesting sounds and gives a hint of what the real instruments are like.
The soprano-ish reed mouthpiece didn't really work for me - I already play alto sax and the plastic reed here is just way too soft and small - but I count the rest as good value. Adding a tube to the flute mouthpiece convinced me that I understood the technique, and I progressed to a real flute. I probably won't play brass but the mouthpieces are fun anyway.
They are essentially a hard plastic shell like ABS with soft rubber (perhaps silicone) grips and mouthpiece cups. They seem well made and feel nice.
I can't comment on the intended use, but I think they're great. If you're curious and can spare the money just get them.