I think first impression is important but not a key indicator of long term success. The first iPhone unlocked the mobile web browsing use case, which is huge. People had always wanted to browse the web, just not on mobile. That alone makes the first iPhone a revolutionary product. Magic Leap One has to create new user behavior, which is much much harder.
I think along with this TOY-ness, YC also looks for the available market and in this case I do not see that with this app. maybe the idea is to get some traction and sell it to Google down the road?
I maybe wrong but I see the email market in two ways: people who have two many emails which creates a scheduling problem. And people who reply/compose too many emails. I think the later market is not that big because you also need to make sure the people get more value (or should I say, write more emails) out of the monthly fees they pay for the service. But I'd like to be wrong here and I wish you succeed. Thanks.