MarcXLanswered grow question 5y ago Canna flush can be useful for overnutrition problems in combination with flushing but normally not needed before harvest, except for the reason you have to harvest quickly.
Kelp-based additives like BioBizz Alg-a-Mic or Green Buzz Liquids Growzyme are also a good alternative for flushing additives.
But for your question, I see no cons.