Matalarata
Arcane
If you can land a hit on an enemy, you'll kill him faster with damage rather than with CON damage. And if you can't land a hit, this item is useless.
You're somwhat mistaken on the item's purpose, It's only drawback is it uses the mantle slot, which is a valuable one, since it increases saves, commonly.
29 DC save means that the usual enemies I find (max 17 Fort) needs a 12 to save vs an action I would basically do nonetheless, attacking. COS damage is always good, because it's exponentially increased damage on HP. Each 2 stat damage you cause, it's multiplied by the HD of your target. Now, stat damage is hit and miss, since not every enemy needs all stats. But CON? Precious few entries in the monster manual do not need CON to live, you don't need to bring their stat to 0 to make their lives worse.
It's progressively going to phase out, and I'd never splurge monies on it (I'm cheap), but I found it at level 10-11 and it's immensely good. Additionally, even once I start hitting 20 Fort saves, they still have a 45% chance to get the effect. It's a very good animal companion item for mid-level imho.
On a sidenote, I finally encountered the first Demon Army my General couldn't defeat all alone just by bringing a single contingent of shield bearer to meme tank the damage. People talk about marksman but those guy really break the early Act III crusade: