On the driveshaft brake, it locks on good, maybe too good to stop a moving truck but holds well for parking. I could see the rear wheels locking up if you weren't used to the self-energizing action of that system. Also, if you had to jack up a rear wheel, it could roll since the brake is on the shaft not at each wheel. With the rear wheels style brake, you apply the brakes as if they would using the hydraulic system to stop a moving vehicle. Also, when adjusted properly, they lock both rear wheels up so changing a tire is much safer when applied.
That's my take on it,
Scott
