I'm curious to try this out, but I can't justify spending $97 for Nerva without any kind of trial period. A promise of a full refund isn't enough, unfortunately.
If you do want a free trial the mobile app store subscription has a free trial but doesn't come with a money-back guarantee (Apple's control).
In your view, what's more compelling - a free trial or money-back guarantee?
A free trial would be far more compelling.
FYI I'd be using this on Android.
If you're interested, you can download the app from the Play Store and try the program with a 7-day free trial. Let us know what you think.