From the beginning there were some glitches (websites temporary unavailable, difficulty to connect my SMTP accounts, etc.) but nothing serious and with the help from the support, I could have everything set up.
The behavior of the warm up was not as expected. It should have sent 25 emails/account/day. For more than 2 days it sent nothing, then it started... with its own rhythm. The analytics from the interface were not congruent with what I saw was sent/received so it was a bit confusing. In the end, besides the strange behavior, the warm up worked fine for all my accounts.
So I decided to set up a campaign. I wanted to organize a webinar and invite some leads through cold emailing. I set up my campaign. I felt I could have use some documentation (there's none for now) but it's simple enough that with the product demo on the Youtube channel, I could find the answers to my questions.
The problem is that when my campaign was finally ready and activated, no email was sent. I reach to the support in web chat. The next day by email. There's supposed to answer in 24h/48h but I didn't get any answer after more than one week. It was almost 10 days when I got an email saying they would have a look at it. It was already too late for my campaign and I had to cancel my event.

It was the end of my refund period so I had to decide. The combination of not being able to send emails and the support being unreachable for barely 10 days lead me to ask for a refund.
It may be a great product when it's more stable and reliable, when they correct the interface glitches, add some docs and reinforce the support. For now, I was not able to use it and went for an other solution.