I like the idea, and in general think it should be an option. The only circumstance where I think I would feel “cheated” as the zapper would be if I was zapping for the purpose of zapvertising, because in that case I am zapping with the expectation that others will be able to see that zap on that post. I believe clients would need to indicate somehow that the recipient only receives private zaps. Perhaps the the zap icon on their notes could have a different look than normal zap buttons.