No one responded to your question, so I will. I used them in 2017 for a Baltic cruise on RCL. I was promised 7 UA miles per dollar spent excluding taxes and that was what I received. The miles were deposited into my account within 3 weeks of the cruise. The price that I received for the cruise was exactly the same one listed on the Royal Caribbean website. I was even able to re-fare the cruise once when the price dropped without any problem. They provided very good customer service.
This summer, United Cruises has been offering a lot of great promotions. Not only do all Balcony and Suite cabin earn 7 miles per dollar spent (excluding taxes) but they were giving free gratuities and a $200 airfare credit for the month of August.
Cons: There is a $24.99 fee for booking any cruise and $100 cancellation fee.