While this is the best root you can get at lvl 70, it is not always reliable with higher level mobs. I have killed many 100s of efreetis (73 - 75)in Jewel while pling alts and while it is rarely resisted, mobs break root early very frequently, sometimes as soon as it is cast. When you have kiting room it is generally not a problem, but in tight quarters like fighting in the pyramids of Jewel, along with its short range it can be risky. I have also used this with the skeletons in LP (77 - 79) with a little better results, and given the large kitting area have not had any problems.
You are better off however getting Vinelash Cascade II (III would be better but Sony has an irritating habit of defining rk III spells that no one can find). It has a shorter duration but is generally reliable against higher level mobs.
Maybe we will get a serious root in next expansion, although what we have is serviceable if you use them carefully.
Edited, Aug 16th 2008 1:38pm by RFHarris