I was very enthusiastic about this plugin as we already monetise many sites via Namely.PRO.
Shame, it appears that once the customer pays via wp-vainity-emails, you get an email and you have to configure the email forward MANUALLY. This is like just a subscription widget, there are many of them on WordPress.org already.
It wouldn't be a big deal. Setting email typically takes 10 minutes of your time. But if you have to do it 10 times a day - it becomes annoying. Trust me, I was there before. You want the things to work for you, not other way around. Then, if the customer wants to change the email forwards, you have to do it MANUALLY again and again.
On contrary, with Namely.PRO everything is done automatically and instantly. Neither you have to be bothered, not the customer has to wait. Also the good thing is that Namely.PRO doesn't charge money as we opted in for the revenue sharing option. We were able to negotiate bigger take from them as they run hundreds of our domain names and help us to resell both emails and sub-domain.
Their solution is like running a real registry, our customers can set nameservers to their subdomains and run it anywhere they like while we are paid every year for renewals.
Also Namely.PRO is much more richer in terms of handy features and flexible in terms of support.
I would have a second look if you would implement all of the above. At the moment, I cannot find a reason to use this plugin.