I have been mining with USB ASIC (100GH/s solo) for four years, but I haven't mined anything.
In theory, mining depends on luck, but in reality it depends on hashrate(capital).
I'm still testing it, and if I can get bitcoins, maybe it's not unrealistic to use USB ASIC mining for decentralization purposes. I haven't got any bitcoin yet though, so I don't think it's realistic either.
You using a solo usb will never see a block, statistically. You need to join a pool.
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This would require a decentralized usb-mining pool. That way users get some revenue and the hash can be aggregated to all users
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