There is a trial, but it's not free. You can pay $2 and get a free trial for one week, while signing up for a plan. If you're not satisfied, You need to cancel the plan before your trial expires (7 days), so that you are not continued into the monthly subscription plan.
Why there is a charge for signup? We get a lots of request via PM in TradingView for trial just like that. These users try one script today and another next day just for the sake. You will be in agreement that no one can judge a script in a day. The only way to keep away shallow testers was to charge a minimal $2 signup fee.