You can buy the 1-month subscription in the app and immediately cancel it afterwards in your Google Play account (https://play.google.com/store/account/subscriptions). Then you'll have a little more than a month to check out if you like it and decide afterwards.
If you need a little less time, the yearly subscription option has a 7-days free trial period (which you can also immediately cancel, in this case you wouldn't have to pay anything).
