I am actually moving from Proton to iCloud. I find using the bridge and custom iPhone app a bit of a pain in the ass. Not to mention, once the emails are in there, you have to figure out how to get them back out.

The security was good, but I find it more practical to just use iCloud. The VPN was nice, but for everything else - I have 1Password, etc..

Look into the lock-in, I was able to sync my mail out over several days using the bridge but some people have had issues getting their email back.