androidin Sorry to say, but device unlocking will now last much longer since every time the second factor has to be given.
That is an expected result of the feature functioning as it should - that is to say, it is prompting you for the configured PIN after authenticating your biometrics. So there's no need to be sorry at all, you're just explaining that the feature is working as intended.
androidin I understand the plus of security but do you expect that this is used broadly?
Yes, this is a highly requested feature for many years now. We expect people who understand why the feature exists and who can benefit from what it provides to use it. If someone wants to distrust the secure element by using a lengthy passphrase with 90 bits of entropy, and also doesn't want to be susceptible to someone like a street mugger to knock them out and use their finger to unlock their phone and run off with all of their data, I suspect they will find this feature extremely useful. Before, they had to either compromise and use a short PIN as their only line of defense, or they had to use a longer passphrase with the secondary method being just a fingerprint. The added layer of protection that this feature provides insulates users and provided a more secure secondary authentication method that will allow more people to be able to daily drive a drastically more secure passphrase. Even if it's a minority using this feature, it will be the people who have a real need for it, just like with other features that GrapheneOS provides.
androidin I activated it and was annoyed after only some unlocks.
If your current primary unlock method is a short PIN, and you use a fingerprint as the secondary method of unlocking your device, I get it - I'd probably be annoyed too in your position. Now consider someone who uses a long passphrase and doesn't even use a fingerprint because of the kind of attacks that can expose them too. From their perspective, this just made their life a lot easier!
androidin Can't really see the chances in activating this.
That's perfectly fine, it's completely optional.
androidin It's frustrating me. What a shame that it did cost so much development resources rather than spending the time in secure face unlock.
I'm genuinely sorry to hear that this is frustrating to you, especially since you follow that up with the assumption that the time used to develop this feature could be used to provide something that we fundamentally cannot. GrapheneOS already did support secure face unlock. It was supported in the 4th gen Pixels that had the appropriate hardware for face unlock to be secure. The latest Pixels don't provide that, and we can't wave a magic wand and make a camera face unlock implementation magically secure.
Hope that context helps!