I'm an experienced cook and this device is useless. The only area where wet measurements really matter is in baking, and even then 5-10% error is more than acceptable. If you really cared, you'd just weigh the liquid and compute its volume from its density (if you're OK with the error of a density estimate).
Error can vary more widely than just 5-10%. For example, the same careful measuring to within 5-10% at 1-cup will result in ~40% error at 1/4 cup. And also, people vary in their cooking ability, especially around reaching out to new recipes. It can be hard to get recipes to turn out right, and sometimes it's hard to tell what went wrong.
Not everyone is experienced. Most people don't have the time to learn how to measure like an "experienced cook"
You don't need to be experienced to level measurements. You need experience to judge the results of your error.