I've had a pair of the individual arched tailgate ramps for years. They were originally a Christmas present from my M-I-L because I spent so much time hauling her riding mowers around.
Mine are rated for 750 pounds each and do what they are supposed to do without failure (so far) but I don't think that I've loaded anything approaching their full capacity.
If your loading into something that's high, like the back of a 4x4 pickup, it's best to use the safety chains or wires and tie them down. When the full weight of what you're loading hits those ramps, the back end of the truck will squat. That's not a problem until the weight starts to come off the ramps and the back end starts to rise back up, the ramps don't come with it and the fingers on the end of the ramps are only about 3" long. They can come close to sliding off the tailgate altogether if they're not tied down.