Not the only one - I started using Nine a year ago, after switching from something else that has been abandoned (I forget the name, but I'd been using it for years because it supported bypassing Exchange security lock down).
Absolutely love Nine - it works marvellously with my own IMAP and SMTP servers, my work O365 etc. And everything in the UI is configurable. I think Nine is actually the only Android app I've ever actually paid for - highly recommended it.
I have licenses for both Nine and AquaMail with the same purpose (operates with work-required MFA via O365+adfs+RSASecureID token) and would highly encourage you to look at AquaMail. If you thought Nine was configurable, hold on to your hat - AquaMail is all that and more, I highly prefer AquaMail to Nine for business email.
I've been using Nine for ages and it's great*. How well does AquaMail work with Exchange / ActiveSync?
(*My only real complaint about Nine is if I try to import more than a few months worth of email history into the local cache it slows to a crawl and starts breaking. I'd pay for an app that locally indexes a few tens of GB of email history and makes it instantly searchable.)
I'm afraid I've never used it with direct Activesync; my Exchange connection has always been EWS/OWA-based (whatever they call the web endpoint now in O365 hosted Exchange).
Absolutely, it works (and has worked) with EWS for me reliably over the years, I've never actually used ActiveSync on my (personal) devices, as that gives my company control (MDM) over my device to remote wipe it. I've used AquaMail for... 8 years? (back when it was just one dev and $5) across all the Exchange movement my company has done.
It did take them (the new owners) awhile to get the O365 MFA support coded in, which is when I purchased Nine and used it for a year or so. Once AquaMail got their code updated to handle that, it was like a breath of fresh air coming back to the client. (the export/import of your settings - which are plentiful - works great, I've also upgraded phones many times)