This is a significant point against picking cryonics, but on the other hand, it does give a convenient excuse for the person to do away with the online persona afterwards without raising additional suspicions and needing to answer any further questions.

Also, the more potential donors you attract, the more investigators you're also likely to attract. If I were designing a scam, I probably wouldn't pick cryonics, but I also wouldn't go for something that attracted as many benefactors as possible because it would increase my risk of being found out.