There's no denying it... This IS the best grip for SMN yet... Also, throughout all the servers, this seems to the most expensive grip out of the new grips introduced in Scars of Abyssea due to the NM which drops this... When building NM key item pop set for Bukhis, Khalkotaur can be skipped since its key item can found in Gold Boxes and the Feet Seals can be obtained by fighting easier NMs.
Spiriel is completely right. Enmity is generated as soon as the JA is used, however potency of the BP is based on the skill you have when it goes off (easy to try this, just unequip all gear right after using Hastega, before it goes off, and you'll see duration heavily gimped).
So having Staff Strap on when you use the JA, then switch to Vox Grip immediately for BPs means lower enmity generation as well as higher skill.
Edit: Same goes for the BP delay vs. summoning skill argument btw.. BP delay is calculated right as the JA is used, so you want Enmity- and Delay- for that, then switch to skill+ before the BP goes off.
This Grip will be the new staple for Blood Pact Ward, Rage, Elemental Siphon, and Avatar's Favor!
That being said, Seeing as how SMN Doesn't rely on TP (Well, For the most part) I wouldn't throw out your Staff Strap just yet!
Idling in Staff for general MP/Enmity purposes and Macroing in this Baby for any of the above mentioned actions would be the optimal set up.
However, Some cases its worth it to keep one grip on (Solo?) So this would be the new full-time for that situation!
@Spiriel:
By those "Full-time" Situation, I meant if you're meleeing, say for maybe staff triggering "Blue" during blunt time, or maybe Earth-Crusher/Sun for "Red".
There are some reasons why you'd want to full time a grip cause you'd need the TP.
Of course what you said is obvious, and i'm not sure why any SMN wouldn't do that.
Finally one interesting grip for SMN besides mage's geral grip. Drops from Khalkotaur at Abyssea Vunkerl but you can buy it for a cheap price on AH since they drop a lot and not much ppl want it.
I totally agree with Spiriel. You must change grips for - enmity while using JA and chance back to Vox grip to get more avatar power.