OP is looking to move away from Google. Immediately getting locked into a different, arguably more restrictive, platform isn't a solution.
Now in general:
Pros:
free(paid plan only?)- company will stay in business for a while
Cons:
- subject to Apple's privacy policy
- US based company, not great for privacy
- locked into a different platform
- Apple's walled garden ecosystem means long term use is questionable. Will Apple keep supporting 3rd party email clients in 1,3,5 years? Do they even support it now? Who knows?
- Apple has control over your account. If they screw you over on an iPhone purchase and you do a credit card charge back on them (for any reason really) do they let you keep your account? Google doesn't