Useful but flawed. Company ignores requests for refunds
Their google marketplace page is flooded with fake reviews so it's hard to judge them before buying.
This addon is pretty useful overall. It's handy if you don't need to send any more than ~1500 emails per day, and want to keep track of opens, bounces, unsubs, etc..
There's a significant flaw with resetting people who've unsubscribed. After removing someone from the unsubscribed list, if you open the tracking report for that sheet the person will be added back to the unsubscribed list.
If you don't have many sheets to search through, you can manually find the contact and edit/remove their entry. But if you have many sheets it would be very tedious, if not impossible to find and edit them.
The unsubscribe button is also super easy to misclick because it looks like "small linked text" surrounded by a bunch of whitespace, but it's actually a large invisible bar that spans the full width of the page.
Deliverability:
When I first tried this app some years ago I had open rates of around 70%. With other popular email clients like Convertkit, Mailerlite, Getresponse, SendPulse, I get 50-70% open rates. I'm sending the same emails to the same recipients.
More recently my Mergo open rates dropped to as low as 20%, and support seemed to have no clue. When I asked for a refund (I just bought it 2 weeks ago and had to drop my sending to 50/day due to the poor open rates) due to the poor open rates and unsubscribe glitch, they've ignored me.