Still, if you have multiple soulmelds giving you natural attacks, the necklace could be worthwhile.
For a 6th level Totmeist that has, say, 6 natural attacks (assuming 3 from Girallon Arms) and a +1 Soulbound necklace that affects 3 natural weapons. He can put 2 essentia in the necklace for a +3 to three natural attacks and 2 in the Girallon Arms for a +2 there, sure he uses up all his essentia, but he can squeeze just a bit more out of it.
The thing about the necklace though is that it can be enchanted just like a magic weapon, and those enchantments then apply to the natural attacks the necklace is affecting, such as keen, wounding, vampiric (+1d6 damage to living, heal that amount), etc.