wholesale on aliexpress
These are not direct-thermal-coupled.
Just a tiny bit better than the “standard” alu ones (which can be bought for $0.06/ea, maybe even less)
Not worth the price IMO.
I don't think it's a bad deal. They are much cheaper then the direct path options, but probably work better than aluminum. I use this type of board on lights that use moderate current. I gouge a small slit down the center of the thermal pad to get some direct path.
Not that much. Twice or so 
They do, but again not that much without some modding like yours.
You can also drill a hole in the thermal pad and rivet a small piece of copper wire there, BTW
Agian, lck-led has some copper stars for $0.75/ea - that’s the same price ($150/200pcs), and you don’t have to buy 200