As far as my experience can tel, MailPoet 3 is. MailPoet 2 I can’t say.
MailPoet 2 was working for me until I tried importing a list of new subscribers this morning. Then I started getting 500 server errors. I temporarily downgraded to 5.x and this time the import went smoothly.
Then I upgraded back to 7.x because my theme really wants it.
PHP 7.3 is giving strange issue and behaviour with mailpoet 2, some white screen,some unusable table
I downgraded to 7.0 and was fine.
Seems it is not compatible with PHP 7.3
If I activate mailpoet 2, I get a whitescreen in admin.
Deactivating Mailpoet resolves it.