The
Regent Symbol of Innoruuk has a casting time of 6 seconds and if Clinging Darkness sticks it lasts for 6 ticks. Resist rate is comparatively high and movement reduction is only 30%. In my opinion it is not worth it. - I tried it on live and here on Blue. On live I had the same problem we will have on Green: Snare and root won't stack for a while. That reduces its limited utility even further.
On a new server it is not a bad item in itself and the quest line is fun. You even get to be a Halfling for a while and you can get more of those Halfling illusion masks later (only 1 charge per mask). But if you really are in an area where you need snare you don't want to have to rely on that necklace.
In LGuk I would have to cast it on a non rooted frog and kill it without rooting it in between before CD fades. But what might that frog do during that time? If I pull with it the frog will do nothing to me before and during the first snare attempt. If it sticks I will have to tank it while burning it down. That was fun with Festering Hags in Unrest but I am not convinced that it would be fun or even possible with a Dar Ghoul Knight, protected by classic gear.
With that casting time and resist rate refreshing Darkness during the fight is probably not a reliable option if I can't convince the frog to check its email or take selfies with me while I busy myself with the necklace. It might be fun to try it, but I doubt that it is a viable long time strategy. - Come to think of it... I am not even sure if the frogs in LGuk are interested in taking selfies.