Yes, you can use it for free. Basic features such as rolling the dice, changing their type and number, and viewing your history are all available for free, and they won't suddenly become unavailable or start requiring payment.
Only when you want to hide ads or use all the sounds and colors do we offer the paid "Premium" option (choose from Monthly, Annual, or Lifetime). There's no problem using the app for free in everyday use, so please rest assured.