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As i understand Leo is using Hiveengine and comments make sure not to spam the feeds. A system that was used well in the past already by another app on Steem. +

I think you're right about the desire to keep feeds clean. I didn't know aboout H-E. Seems to me that the threads are simply Hive comments to posts like https://peakd.com/hive-167922/@leothreads/leothread-0-6 which become filtered on the threads front end. Yours is at https://peakd.com/@lordbutterfly/re-leothreads-76cubh, but I don't know. Even if H-E is used, the comment/data does seem to end up on the main chain.