For custom jsons it doesn't matter, user doesn't lose his STEEM only some RC amount so it can be retried.
I've never noticed the chain reorg during custom json processing. I've processed many of transactions and no issues reported.
Transfer transactions are streamed from blockchain in the background process. So I never lose them.
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RE: Is Custom JSON the Future of Steem? | The one thing that has been going up on Steem in the bear market!