My experience with /e/ OS has been good so far and yes you're right, I'm using MircoG and yes, all my banking and payment apps are working fine, Just Uber does not work. Google Maps work fine too with MircoG on /e/ OS.
The main advantage /e/ OS has over other custom ROMs is it's 'Advanced Privacy', which blocks all the trackers from all installed apps at device level (by blocking DNS request). It is very unique to /e/ OS and it works like a charm. You can find more details about it here: https://doc.e.foundation/support-topics/advanced_privacy
And No, /e/ OS does not focus only on pixel device, it's much more flexible than Calyx or Graphene.
For my device, Easy installer support was there, so installing /e/ OS was easy. I have also installed it on my friends POCO F1 using TWRP recovery. You don't have to build it yourself, /e/ foundation hosts pre-built images for all supported devices.
How did I do it without Easy Installer?:
1. Go to this link: https://doc.e.foundation/devices and check if device supported or not
2. If yes, copy its codename (For POCO F1 it's "beryllium".
3. First check if there is stable release for your phone with this link: https://images.ecloud.global/stable/<codename>/
4. If not, then download dev build for your phone my modifying above link to: https://images.ecloud.global/dev/<codename>/
5. You can find ".img" file of recovery and ".zip" file for build.
6. Refer this video to install /e/ OS using TWRP: https://www.youtube.com/watch?v=TZyqFzsXYek