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The only thing I don't like about your option, Kosha, is the gray salary. I myself work in a company that's roughly like the one you described, but it's solid enough that I don't have to worry about it; the salary is official, and there isn't much cult-like behavior. Well, and corporate events – a very important part of socializing with peers happens during them.
Go to the interview; maybe you'll realize at this stage that it's a scam, or you simply won't pass the selection process.
By the way, if it's really a European office, the dependence on this thing is huge; I recommend it.