[tummybug]

I would argue its second most popular feature is purchases on dark net markets. This has been a constant theme since bitcoin was first released and I think is always discounted when talking about the currency.

[DrAwdeOccarim]

Is there a way to reliably figure out the GDP of dark net markets?

[Cthulhu_]

Kinda; if the dark net markets have known wallet addresses it can be looked up and analyzed in the blockchain. Or if the other public addresses are known, transactions can be deducted from them.