MarcXLanswered grow question 5 years 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.