I’ve been running my own mail server using Mail-in-a-box on a digitalocean VPS for about 10 years. I also pay for an external SMTP relay service because I still get randomly blocked by Google/Microsoft/whatever just by virtue of having a digitalocean IP.
Total cost is $15/mo for the VPS and $50/yr for the relay service.
They’re likely not fake; odds are there are loads of people who will buy this product and never have an issue. The problem is that some small percentage will experience catastrophic loss, and who wants to roll those dice?