I spent three weeks being passed back and forth by one bank being told I needed to speak with they other bank. They confirmed the money had been debited from my account, and confirmed it was not deposited in his, but nobody could tell me where the money went. I called Zelle multiple times, but all they would tell me is I needed to talk to the banks. Eventually after three weeks the money was quietly returned to my account with no explanation. After a bit more digging it appears my transaction triggered some fraud alert, but neither myself, the depositor, or either bank was notified of this.
To add insult to injury, during this process the people in charge of Zelle at my bank (which rhymes with Space) told me I was out of luck, because using the Zelle for any type of commercial transaction, including sending rent or security deposits, is against the terms of service. Looking back over the terms of service I found they were 100% correct.
I also found that Zelle is basically just a front-end for the existing ACH Direct Deposit system. It was created by a consortium of banks to compete with services like Venmo, but it at it's core a very different service. Venmo actually provides value by acting as a middle man: Venmo pays the recipient and collects the money from me. Zelle is just a way to send money directly to someone's checking account, but by using their email address or phone number instead of the account and routing number. This is why there is absolutely no recourse if anything goes wrong.
tl;dr do not ever use Zelle.