Too bad you missed it, there was another thread about this yesterday or the day before.
It's a Sierra Precision Rifles grip.
Yes, it is a great grip. Offsets the hand so that it is positioned better for proper placement of the tip of the trigger finger. It has a thumb shelf on the left side of the grip though so it's really not an ambidextrous grip. The right side of the grip has a built up pad that can be filed or trimmed down as the user desires.
Oh, and it is a FAT grip. Really increased diameter over that of an A2 grip, all my target rifles use the things.
[url]http://home.bak.rr.com/varmintcong/ar10/AR10A4cl.jpg[/url]
[url]http://home.bak.rr.com/varmintcong/ar10/AR10A4cr.jpg[/url]
Links to a little closer up pictures of both sides of the grip as installed on my AR10.