Indeed, I wouldn't suggest it be to easy to find either.
If it was able to drop from Nihalthak it would have to be extremely low chance to drop.
Crucible would be another good place for it since there are Nihlathaks in there also.
And now that I look at it again, the Increased Energy could be 10-20% so that more stats vary.
Or possibly even the FCR or the FHR or both, but glad you like the idea Sleezy.