Try it before you pay
You can use Buildsavr without paying and without a credit card. The free plan gives you a set number of comparisons every month, with no time limit. That is how you check the tool suits you before taking out your card.
The Builder Homeowner and Builder Pro plans add a free trial of 7 days. A credit card is required to start the trial, but nothing is charged during those 7 days: Buildsavr gives you the trial period at $0 so you have time to cancel. You get a reminder email at least 1 day before it ends.
By starting the trial, you agree to be billed when it ends unless you have cancelled. If you cancel before the trial ends, you are never billed. If the trial runs its course, the first payment is taken and the rules below apply. The trial exists precisely so you decide before you pay: use it.