I have not sailed RCCL, so I have no knowledge of the cost and coverage of their insurance.
On Princess for our first five cruises we found cheaper cruise insurance by using an independent company. After five cruises on Princess they then offer a free insurance upgrade. So after five cruises it became became cheaper to go with the cruise line insurance.
If you decide to go for independent insurance be sure and check out the reliability of the company.
Most importantly, whatever you decide, I strongly recommend purchasing insurance for any cruise.