This is unlike most fish sauce you'll find in many Asian restaurants. Generally, I've found fish sauce at restaurants to be sort of sweet, a little mild - something to perk up the food without being as salty as some soy sauces can be. Most supermarket brands are made with 'anchovy extract', and have some sugar it them.
Red Boat Fish Sauce has a LOT of flavor to it. And, there are only two ingredients: anchovies and sea salt. That's all.
Because the flavor is a more intense than many other brands, I've had to adjust the amount I use in recipes. The taste isn't overpowering, there's just more flavor than some brands. The difference is similar to the difference between regular soy sauce and Tamari: there's just more flavor, so you use less. (And, like anything in cooking, it's always better to start with less, then add more if needed.)
I found that if you're using it for something that's going to end up being in the fridge overnight, the fish sauce taste intensifies and can overwhelm some of the other flavors. So, adding less at the beginning is helpful.
