You should never trust ANY secondary braking system. If it is life or death or you have a chance of losing your rig, don't trust any of them (or any combination of them). Line locks work awesome for temporarily holding a vehicle in place, but don't leave them set for weeks at a time (again, they will drain your battery, bleed off pressure, and put excess strain on brake system components). If you need something as a safety device on the trail/short term parking brake, line locks are probably the best way to go. As far as the safety of running without a "mechanical" secondary brake, the master cylinder is divided into 2 partitions to ensure that at least one set of brakes is working. Legal or not, between downshifting and having at least one working set of brakes, I'm not worried about missing out on an emergency brake (they don't really have any braking force anyway).