I've heard good things about it, for sure, but I'd argue that it isn't really an Email client. It is a Gmail client as it doesn't work with anything else. Fastmail is in the same bucket, but it is part of my contention about there not being good Email apps generally.

It’s really tempting - uses their API for that speed.

I’m worried Google won’t like it someday. It’s such a hassle if they shut you off that I want to seem like the most normal user to them. Pay Mimestream, skip ads, avoid Gmail app telemetry… any incentive for Google to permit it longterm? (Like maybe you’d switch to Fastmail if they killed Mimestream… or maybe not!)

Why does it seem to take so long to get & read one new email?

I can use get new mail or synchronize in Mail.app, but always spoiled by the instantaneous Gmail app notification. Often don’t have patience to wait for Mail.app for 2FA codes (just OCR or manually type from the Gmail notification mirrored on Mac).

Also should back up a bulk of ancient emails clogging the app, might be partially my fault.

Mail.app's search is completely and utterly broken in my experience on Macs and on iPhones.