Typically they only lock up during acceleration and when using the engine as a brake. My (powertrax) locker will only turn the inside wheel when cornering (unless I stab the gas - then it locks in). Not 100% sure of the differences between lockers other than the fact that detroit lockers are noisy where the powertrax (richmond) lockers are quiet. Most lockers run $400-$450 and in most cases the powertrax is a simpler install - goes in like a mini-spool. They're also much more durable than a posi unit.