Like the title say, I've always heard that, but I tried it but I can't really tell. So is there any scientific evidence for or against it?
From the first article...
Before people learned to brew coffee as a beverage, they ate coffee beans to get a boost of energy for hunts or while farming. Eating coffee beans has the same effects as drinking coffee. However, the effects are magnified because eating the beans provides all of the caffeine and other chemicals in coffee, not just what manages to drip through the filter. In addition, the active ingredients in coffee beans are quickly absorbed through the mucus membranes in the mouth.
The second article talks about the amount of caffeine you can get from eating coffee beans.
An average cup of coffee is made from approximately 25 beans and contains 75 mg of caffeine. So the brewed value of each bean is about 3 mg. However, when you eat the bean, the amount is a little higher.
Even though neither article directly states the amount of caffeine that you will get, if you combine the information in both of the articles they state that you will get more caffeine as well as the other chemicals and nutrients of coffee by eating or chewing on the beans vs drinking coffee.