If it were just a “whatever” new feature on a normally priced phone then sure, a .3 slower unlock doesn’t matter. But this is the flagship feature on a $1000+ smartphone. Its price demands that it be not “as good as” what it replaces (let alone slightly slower!) but demonstrably, clearly superior. And I’ve seen nothing to suggest that.
Face ID is more secure (an academic difference; in the real world, nobody’s fooling either technology), but slightly slower (also an academic difference). It’s better in some cases (wet/dirty hands) but worse in others (face partially covered/strong direct light).
So if they just slapped this on the iPhone 8 at the regular price point, I’d be fine with it. But as “the” feature on a $1k phone, I find it underwhelming and basically no better than what it replaces, just different.