Should be part of the toolbox of all drivers

Exceedingly convenient and easy to use, a brake fluid tester (even if it only tests the humidity of it) proves an indispensable tool.
Did you know that the brake fluid is hydrophilic, meaning it loves water, and more water content increases (which happens very quickly if your circuit is not perfectly sealed) plus your liquid brake is likely to boil your brake and thus become very uncertain. Indeed, a brake fluid should not be changed after a certain mileage or a certain period, but only based on its moisture content.
In short an indispensable tool for quickly saving you unnecessary fees or an unsafe situation.