That aliexpress device doesn't tell you what wattage or data speed the cable will max out doing. Just what wattage it's currently doing (to which you'd need to make sure that the device you're testing with on the other side is capable and not having it's own issues). Also can't tell you if the cable is have intermittent problems. If all you care about is wattage, then fine. But I find myself caring more about the supported data speeds and quality of the cable.

But yes, I agree that cables should just be marked what they're rated for... However it's possible well built cables exceed that spec and could do better than they're claiming which just puts us in the same boat of not really knowing.

Edit: oh! and that aliexpress tester is only 4 lines(usb2.0 basically)... usb 3.0 in type c is 24 pins... You're not testing jack shit on that aliexpress. The device I linked will actually map the pins in the cable and will find you breaks as well.