Transactions are never free. If they are free, you are the product.

From Primal's Terms of Service: 
Transaction fees for incoming and outgoing payments within your Primal Wallet are a combination of bitcoin network fees, fees charged by Primal's affiliates (if any), and fees charged by Primal (if any). Transaction fee policy is subject to change without notice.  

 Any plans of integration with npub cash? 

 As soon as I figure out how to make sure people cannot lose their tokens.