If you choose not to subscribe, you will not have access to most features in the app. You can of course still use the app, but to a limited extent.
The features that work without a subscription are:
Demo account
Weekly allowance
Chores
Instead of savings goals, you can create wishes (not as interactive)
With a subscription you also get:
The ability to connect a bank account to get the most out of the app
Superskills Adventure
Quiz about money
Savings target
Evaluations of transactions
Bonus
If you choose not to upgrade, your existing savings goal will be converted to a wish after the transition period. The bonus will be reset to zero and any bank account that has been connected will be disconnected. Earned stars remain for the children.