At my employer, some users register with a pm.me email address. When users contact us via email, they use a different protonmail address and never the pm.me address. I know you can never rely on the sender address, but from a support perspective this is still strange and extremely troublesome (for example it is tedious to assign the user to an account). I assume that Protonmail users can only receive emails with pm.me, but not send them. For me actually a reason to block pm.me or to handle it like a throwaway address.
In ProtonMail you can have email aliases (different address for the same inbox). By default, user@protonmail.com and user@pm.me exist. You can both send and receive from them.
> to block pm.me or to handle it like a throwaway address
How is a pm.me address more throwaway than a GMail one? I would say it's the other way around, especially considering that many ProtonMail users pay for their email service, so it's more likely to be a real user behind the address.
My criticism is: You should never use an e-mail address from which you cannot send. This has nothing to do with Protonmail but is a problem in general.
> but sending emails from a @pm.me email address requires a paid account.
Forgot that, I personally have a paid account and I think many people using Protonmail do, the free accounts are not so good.
> You should never use an e-mail address from which you cannot send.
Depends for what, if you subscribe to newsletters you don't have to send emails, but I agree it's pretty dangerous to use an email that you don't have send access for.