They come off as a very dodgy company willing to twist the truth themselves. They claim that they can provide E2EE for email, being careful not to give away the fact that this is impossible for regular emails to non-PM customers.
Frankly I only use them because they're the biggest "private" email service and that provides a kind of safety in numbers.
While I concur that it's a bit misleading nothing is stopping you from using your own key and mail client (albeit with their "bridge" solution) to send E2EE e-mails.
If you rely on the keys they generate you can export them and use them accordingly but one should be weary of the handling of said keys if they were compelled to make a backdoor as others have noted.
That being said this does leave a bad taste in my mouth.