Front one ways allow your front wheels to spin in one direction. While on power, your RC will drive like a 4wd car, and off power or braking, it will act as a RWD car. When you break or slowed down, the front wheels will free spin as the bearings only allow them to spin forwards. This makes it act kind of like a super powered spool, where you still have differential action, but neither wheel spins slower then the other. The result is the front gets dramatically more power to the ground. giving you a lot of turning power. Also, as it was said, off power and breaking, you RC will act like it has E-brakes, allowing you to kick the rear around when you otherwise wouldnt be able to.

To clarify about how they still act as a diff, as a spool, both wheels spin at the same rate, no matter what, which will always cause slippage and under steer. A diff works by differentiating the friction or grip between the wheels, and slowing down the wheel with the most grip, while the wheel that slips will speed up. This makes sure theres always equal traction between the two, but the result is a net loss in power on that end, but also the car will wish to pull straight by doing so.

A front one way allows neither wheel to spin slower then the other (as they act like a spool going backwards) but, because they free spin forwards, they will be allowed to speed up. The result is that both wheels cannot spin slower then the front one way, but when they enter the turn, the outer wheel will speed up (rather then either lose speed in standard diff action, or slip in spool action), so you maintain more power with out the front slipping. The end result is that your car will be aggressively pulled through the turn. However, because of how they work, you lose your 4wd breaking on them, which is a perk and a downfall depending on how you want to use it.

I love front one ways personally, but you have to understand that they accommodate a different drive style. You dont have an effective way to brake anymore with out spinning out, but you can achieve a drift at much higher rates of speed, or in situations where you would otherwise not be able to break loose. Also, they allow a greater control over your drift angle mid drift. Say you enter a turn too hard, or at the wrong angle. Rather then either slowing down or slamming into the wall, you can tap the break, increase your angle, and power through the turn.