they are gold plated and the plating is very thin and wears off over time (short amount of time), a lot of people don’t have any problem playing with even bare brass mouthpieces , there are many brands of those, like lebayle, (it is not like sucking on copper) but California (the fussiest place on earth when it comes to these things) has made a point to make the content of lead in brass even less than it is now.....
If you're worried about the lead content of brass, contact the manufacturers and see if they're using lead free brass - most of them use lead free brass nowadays. If you suffer from metal allergies, there's always hard rubber or plastic.
It's a modern gold plated STM. Wafer thin gold plating. Lots of them have lig marks on the top, as the Link lig is unbelievably crap, so people use Rovner type ones, and the screw marks the ridge on the top.
Used value is something in the range of £40-£70 on eBay, depending on how many bidders there are on any particular day. I play a modified one on tenor (10 with a big baffle and some table flattening and rail work). I wouldn't pay over much for a standard one though.
They are far more popular on tenor than alto.
You might have to try 10 of these to get a good one,the older the mouthpiece the better especially if you get into the Early Babbitt's and Florida's,as jonf has said this is a modern link and he is spot on with his value.