Is anyone building Stripe Apps?

Stripe has had the possibility, for a couple of months now, to build apps that can easily integrate with a Stripe account.

It has its own marketplace: https://marketplace.stripe.com/
And the docs at: https://stripe.com/docs/stripe-apps

In principle it sounds good to be able to tap into a quite broad user base and building a simple app should not be as hard as building a full SaaS (a lot of the details are handled by Stripe).

But is it worth it?

Wondering if anyone has a first-hand experience with building Stripe Apps?