FastMail's Calendar is pretty OK for my needs. Google Calendar is better though. But I don't miss it.
Personally I found it hard to migrate to G Suite after being off for about 3 years and couldn't do it.
For example FastMail is less featured, but the web interface is really responsive and the keyboard shortcuts are better. Whereas Google Admin is a nightmare and GMail has gotten really sluggish in the latest iteration for no good reason.
GMail has labels, many people are addicted to those. But regular IMAP folders play better with desktop email clients and I prefer desktop clients. GMail's labels are cool for classifying stuff (e.g. My Projects), however IMAP folders are good for separating the junk. For example I don't want Mailing Lists in my archive.
G Suite has many limits that bother me that do not apply to FastMail:
- Limits maximum IMAP connections to 15: https://support.google.com/mail/answer/7126229?hl=en
- Limits bandwidth: https://support.google.com/a/answer/2751577?hl=en
- Limits maximum number of user aliases to 30: https://support.google.com/a/answer/33327?hl=en
I have hit all of these limits at some point.
FastMail works with something called "sub-domain aliasing". So if you have `user@domain.com`, you can come up with addresses on the fly, like `google@user.domain.com`. I do that for every online service I use. And the web client is friendly to that too. E.g. you can define "wildcard identities" or you can set certain identities to be used per folder.
Sadly Gmail only supports "plus aliasing". This is weaker because it's easier to remove the alias and because many websites, including big names, do not accept "+" as a valid symbol.
You can configure G Suite to redirect all email via a regular expression, so you sort of have it, however it doesn't work if you want to also send email, which you need to reply for support and stuff. This is because Gmail will not sign your emails with DKIM unless the email is a genuine user alias, no dynamically created email addresses allowed, except for plus aliasing.
Speaking of which, even when you send from a legitimate user alias in GMail, GMail will leak your primary email address via the Return-Path and other email headers. This means that user aliases in GMail do NOT work for maintaining privacy. For example one practice I have is to create a throw-away email address that I put on my blog. I don't want my email to get in the hands of spammers via my website. And I get contacted via it and sometimes I reply. Personally I don't want my primary email address to leak when doing that, but that's what GMail does. And I'm not even mentioning that adding email aliases is freaking painful, as you have to add it once in Google Admin and a second time in GMail's web interface.
Basically GMail is useless if you want to have multiple email aliases.
Another use-case I have for FastMail is to send email from my own VPS. I have two VPSs actually and I want them to send emails on important events. FastMail allows me to set a "SMTP only" password. And in case my VPS gets compromised, theoretically at least the attacker will not have access to my email archive. And FastMail's limits on sending email are pretty relaxed. You can send notification emails from your own VPS without worry. Just don't send spam as they'll probably react to that.
It's ironic, but for all of GMail's praise, it's actually pretty bad at handling email.
Also, not sure what exactly you're using from G Suite, but Google Drive is absolute trash for synchronizing files, including its File Drive Stream, its latest iteration. I've seen it ignore updates, I've seen it generate conflicts, I've seen it corrupt content. Google Drive is good for its web functionality, but you can't rely on it to actually copy your files. If I fear the desktop sync will corrupt my files, then I cannot use it, sorry.