Not everyone has or wants to use Face ID, so this doesn’t apply to all users. It certainly doesn’t apply to me.
There’s no option to log in without any further verfication needed. Until you can do that with N26, it’s impossible for it to be as frictionless as with Monzo.
I will grant that Face ID makes for an improved offering over PIN or pattern, but frictionless? No.
I imagine this feature will work with Touch ID also, and whatever biometric security is provided on android devices, as it simply pulls from an API to achieve this, same as Monzo when you enable it. I personally don’t like having the app login immediately with no security check first, so this is the perfect middle ground. And by definition, it is as frictionless as it gets.
If your device lacks these features, then of course Monzo is going to a more frictionless login (at the cost of security unless no one else ever accesses your phone and you have 2 factor authentication on your email), although it’s looking like that will change in the future.
You’re correct, no-one ever accesses my phone and my email is authenticated. I consider this kind of friction when access apps to be privacy features, not security. Two reasons: 1) the Monzo app can’t be used to transfer money without my PIN anyway, and 2) email is much more vulnerable to attack but no-one ever asks for PIN/pattern/biometric locks for their Gmail app 
I have no issue with people who want these checks as an optional feature, but I very much appreciate how Monzo realise it’s not necessary to force on people*
*aside from the legislation-mandated occasional check on customers by asking for their PIN every so often, granted. But I realise that’s down to the law and not to them.
I completely agree with you here on the legislation. I personally don’t like it, and I despise security theatre for the sake of looking secure. With that said, I take my privacy extremely seriously, and I consider my transaction history, and bank balances private information, so I have FaceID enabled for authentication in Monzo too. So do banks, that’s why that information is encrypted by default.
In terms of email, that’s an unencrypted communication platform. Unless you and your recipient are both using PGP or an alternative you should not assume your emails to be private, because they’re not. So having that kind of security to access an email app is relatively pointless, although some email providers, like Proton do implement that additional security step. Alas, things like email and private messengers that come bundled with a device or often tied to that device and are apart of that service, so it’s natural for logging into your phone to authenticate these services. A bank is a separate service however, and as such should have it’s own separate authentication for good privacy and security practices.
With that said, I like how Monzo is trying to innovate here, by doing away with hard to remember passwords, but with iCloud Keycachain, it’s not really solving an issue for me, and potentially makes users without 2fa vulnerable to intrusion.