It says it increases the duration of your Rip by 4 seconds. Does that imply an increase in damage, or, as I suspect, does it just spread the same damage out over 16 seconds instead of 12 seconds? Assuming that's the case, I guess the theory is that longer duration is good because it's less you have to worry about refreshing a bleed effect for your Shred? (assuming Rend & Tear's 20% boost to Shred damage...) I guess it also spreads your generated threat out over a longer period of time, but I can't imagine that being a noticeable benefit.
All in all, unless I'm missing something it seems really lame compared (for example) to the Rake glyph which adds the "prevent targets from fleeing", which is cool in my book.
Edited, Oct 22nd 2008 11:53am by JeeBar