I have spent a lot of time recently trying out various browsers. I want to give you a summary of common findings with Chromium-based browsers, so you can make the best one.
1. Blocking all requests for Notifications, Camera, Location, Microphone should be enabled by default. Websites heavily abuse these features. The options for these settings should be in the Settings menu. By default they are under Advanced > Site Settings, and that means most people won't discover them.
2. Sync must be feature-complete. All Chromium-based implementations start with Bookmarks only and that's extremely demoralising, but I understand why it's the case. Lack of login sync is what causes most users to abandon a Chromium-based browser. I know it's on your to-do list, make sure it's at the top.
3. Ad blocking and tracker blocking must be just as effective on Android as it is on Windows. This means you must sync any security & privacy related settings - e.g. privacy tracker blocking, third-party cookie blocking. It also means you must sync extensions, e.g. ublock origin. Show us you value our privacy, please.
4. USP features are BAD. Whether it's Brave's Basic Attention Token and so-so Shields, or Vivaldi's UI or Updater Service, the addition of non-essential features into a Chromium-based browser results in bugs and performance not being prioritised the way they should. There's a trade off, and the only way your browser takes off is if it's first and foremost a great browser.
5. Test on multiple monitors.
6. Don't install Adobe Acrobat by default.
7. Don't leak data to third party services. I realise you're probably going to default to Bing, which most people will find annoying because it's not a great search engine, but you absolutely must not be collecting data on users searches, whether that's via the address bar or home page. Same applies to sending URLs to a service for blocking dangerous sites. Don't collect data on us. Privacy by default please.
8. Make the scroll bar dark in dark mode. I haven't seen a single Chromium-based browser get this right yet. The world's full of users in dark mode with a light scrollbar down the edge...
9. ublock origin is a must-have extension. Whatever Google does to try and disable it, you must not do the same. If ublock origin stops working for some reason, you'll lose all your users to Firefox, making this all a waste of time.
Google is planning to restrict modern ad blocking Chrome extensions to enterprise users only. ETA unknown. This is one reason why it's important that Edge gets good ASAP.
USP - Unique Selling Point. Browsers add features to try and differentiate from other browsers, but those features end up sucking dev time away from the core browser functionality. The more of these features in a browser, the worse it ends up being.
Adobe Reader is installed automatically by Chromium. If you uninstall it you can still read PDFs, there's a PDF reader in Chromium. It's just a pointless install of third-party software, like the Ask Toolbar, or Bonzi Buddy.
Thanks for mentioning DNS66, that's interesting. However, I still think the browser needs to block ads because it's the browser that exposes the user to the ads. Relying on Android, or on the user to have installed something like DNS66 doesn't seem fair to less tech-savvy users.
10. User Agent dilemma. - If you leave the User Agent as Chromium, everything works, but people can't measure Edgemium rising in popularity. - If you change the User Agent, you'll trigger loads of websites saying "you should get a modern browser, click here to download Chrome". I think this is the option you've chosen.
I wonder if we can do better. Websites shouldn't be doing different things dependent on User Agent. There isn't really a good reason for User Agent to exist at all. Perhaps you can invent a new way to track browser stats without having to disclose User Agent in a way that breaks poorly-coded sites. I don't know the answer, but User Agents have been a problem for as long as sites have tried to use them for things.