Join the TestFlight
The Just the Links beta is free. Install it through Apple’s TestFlight app on your iPhone, iPad, or Mac.
During the beta you can try any of the purchase options — monthly or yearly — without being charged. Apple treats in-app purchases as free while you are testing, so you get full functionality for the length of the beta build.
When a build expires or you move to the App Store version, those beta purchases do not carry over. You will need a real subscription then.