I'm not clear about what you're asking. If your United Visa already provides LDW for car rentals, why would you care about what some other card provides? Is there some reason why you would prefer not to use your United Visa?

By the way, credit-card LDW coverage tends to apply only if you have declined CDW coverage offered by the car-rental company. If you accept any form of optional CDW coverage offered by the car-rental company, I don't think any credit card will provide LDW coverage for that particular rental. On the other hand, if the applicable law in the renting jurisdiction limits your liability to a certain amount (say, 700 Euros), then I think that credit-card LDW coverage would apply.