I did the 30-day free trial one time bc we were ordering Domino's and wanted free delivery (lol). At the end of the 30 days I cancelled it, no questions asked, no fees charged. It was totally fine.
Then a few days later, I got an email offering me a free 12-month membership. So I took them up on that and am still enjoying free 2-day shipping from several stores AND free delivery from Domino's ;)