Revolut Ltd is regulated by the Financial Conduct Authority of the United Kingdom and has a banking license. It's a very safe payment service with fast transactions with low fees.
You can use the Revolut app only after you've entered the corresponding pin. Payments also have to be confirmed with one-time pins that Revolut send you to your phone, email or call.
Your Revolut card is safe to use for payments, however, it also allows for contactless payments or smaller amounts, so as long as your card is safe and not in the hands of unauthorised persons, you won't need to worry. Larger terminal payments have to be confirmed with the card pin.