Tidbit: Monetize without ads. Let your visitors help you mine Bitcoins

It's not clear to me whether the user is aware of what's going on ("let" implies the users have a choice but nothing in the copy affirms that)

If they do, this could be cool: I'd happily run a bit coin miner while reading an article rather than hitting a paywall. But if it's done without my permission I'll be upset when some rogue tab drains my battery.

Seems very interest and I'm actually considering using it except I have two questions, will this lag mobile or slow computers? And since I'm working on a chat web app which uses sockets will this affect it in anyway (eg. Lag)?