Regarding appearances, try going to the Play Store, do a search for email apps, and in each one there are some screen caps showing you a general look and feel of the app's user interface.
Also, apps like the Gmail app get regularly updated so basing its current performance on previous usage might not apply.
(That said, my default email app is K-9 Mail, an Open Source app with a long history. Also recommend ProtonMail, an email app focused heavily on security and privacy issues.)