I loathe apps that want a subscription for such a trivial concept. Why did you choose this route over ad support or one time payment?
Forgive me, but if the market responds to OP's subscription model (and $4k/mo is not trivial), no ads is a better user experience and there is less dependency on the ad network for revenue.
It's typically much harder to acquire new users than retain current users = subscription model allows you to monetize your userbase over a broader period of time (let's say $5/mo * 6 mo = $30) to a value that would likely be cost-prohibitive. Most users would not spend $30 for this app. But they might sign up for a free trial, and then the $5 subscription.