My big problem is that this is worse than useless.
I started doing unique-address-emails back in probably 2002 or 2003 and did it for around a decade before giving up.
A couple of times per year I would start getting spam or similar on an email address and would know exactly what had been breached and I would try to notify the companies involved. I'd probably spend an hour or two finding emails for key contacts and send a few paragraph email explaining how I knew they were breached etc...
90% of the time I got absolutely no reply whatsoever.
5% of the time I got a pleasant reply and someone said they were already aware or they would look into it.
5% of the time I got confused emails from a non-technical person that didn't understand how their PHP shopping cart software which hadn't been updated in 2 years got hacked, and didn't know what PHP or Linux or anything else was because the neighbor's kid had installed the site one time 2 years ago and now was too busy in college and why are you bothering us about this we have orders to ship!
5% of the time I got incredulous replies from technical people who insisted that I was wrong. That email address must have leaked some other way!
Then there was the last time I ever sent one of these emails. I guess I had found and emailed the owner of a company to email who had then added in his tech person. I explained why I had huge confidence something on their side was breached, but, couldn't explain to them what or how. They eventually got rather hostile about it, first accusing me of extorting them for the information (I never asked for money, but bounties weren't really even a thing back then like they are today). Eventually culminated in them adding in their lawyer with more threats and demands for my full name / address (presumably so they could actually sue me). I ignored them and fortunately the whole thing went away.
That was the last time I sent a report about one of my emails being compromised and shortly thereafter I stopped using tagged addresses entirely.