I use full Lockdown sets in all of my Time Corruptors, primarily for the ranged defence and find that the proc fires quite often. Also it doesn't just stack on bosses but also fires independently on minions and lieutenants. The animation for the hold in Distortion Field is a bubble around the head of the critter, the animation for the Lockdown hold is an electric bubble like the sleep from Electricity.
I ran a test a short while ago with and without the proc to confirm this.
My advice would be to take Distortion Field, not only is the slow good, the hold is decent especially with the Lockdown set and you can stack it multiple times.
Take it and love it. 🙂