This is totally anecdotal, but I (and apparently many other people online) have had pretty terrible experiences with Zelle, moreso than I've noticed with other fintech services.
A family member tried to send me money, which used to work perfectly fine via the bank's older transfer methods (including PopMoney), but once the bank switched to Zelle they somehow lost the transaction completely because my bank had yet to integrate with it.
Zelle's app and help pages were terrible and directed me to create an account and download the app to get the money out. I did that and the money was still nowhere to be found. The bank customer service wouldn't touch it because it was Zelle's fault, and my family member apparently had to wait on hold for an extremely long time with Zelle to get it sorted out and get the money back in their account. I can only imagine how much of a nightmare that could have been for less financially-secure or tech-forward people.