MrMonkey

It’s bad on Android, but is good on desktop

No ports open to the internet except 80/443 on the reverse proxy

In terms of security, isn’t this kind of the same as just opening the server port to the internet, which many others are advising against?

Correct, aliases are one of the best built-in features. Unlimited aliases costs covers a decent part of the subscription

If you are referring to ProtonMail encryption, i think it’s primarily about encryption at rest, so that nobody except you (not even Proton) can read your emails. Unlike other email providers (like Gmail) where the emails could be easily accessed by the email providers whenever they want/need to (like data for ads or legal orders from government etc). While not at rest (i.e., sending/receiving emails), emails between Proton and Gmail are on TLS unless it changed in recent years. If the email is password protected in which case Gmail cannot read the email until you open it with the password

ProtonMail has a free version which is enough for many. Every email you send or receive in Gmail is being collected as data by Google and i don’t want to give my personal data to Google