That's a very niche app. Niche in the sense of "how many people are going to pay $180 a year for an email client?"[0] $99 a year for Hey.com is steep for most of the population. I honestly can't imagine someone paying double that for something most people get for free.
[0] It does a lot more than email, and for that reason may be worth $180 a year, but you present it as an alternative for email.
[0] It does a lot more than email, and for that reason may be worth $180 a year, but you present it as an alternative for email.