The Great Claw on Possessed gives +1 S to an attack, but you also get an extra attack as well. For your 50g you essentially bought another attack. According to a Possessed starting stats and the text description, a Possessed model would have two regualr attacks at S4, and one attack with the Claw at S5.
The reason why I'm asking this, is that every place I've seen where they talk about Mutants getting the Great Claw, they are screwed over and the Claw is made to function like it was simply another weapon. Give a Mutant hammer/dagger, he attacks twice at S3 (3g for his weapons). Give him a Great Claw and a dagger, he attacks twice - one S3 one S4 (50g for his weapons). Anyone else see a problem with this?
Let me go one step further.
No Mutations: Possessed 2 attacks at S4 for 0g; Mutant 2 attacks at S3 for 3g (hammer /dagger)
Extra Limb: Possessed 3 attacks at S4 for 40g; Mutant 3 attacks at S3 for 46g (2 hammers /dagger)
Great Claw: Possessed 3 attacks 2xS4 and 1xS5 for 50g; Mutant 2 attacks 1xS4 1xS3 for 50g (dagger)
Possessed: Extra Limb vs Great Claw
For 40g you gain an attack
For 50g you gain an attack at +1S
The extra 10g buys you an additional S on your extra attack
Mutant: Extra Limb vs Great Claw
For 43g you gain an attack
For 47g you gain +1 S on one of your attacks (you do not gain an attack as in the 43g above)
The extra 4g you lose an attack, but one of remaining is at +1 S
Umm, that sucks.
So, Great Claw: 'Great' for Possessed; 'Not So Great' for Mutants.
In fact, if you have a Mutant with that mutation, that's how you should write it down...
'Not So Great Claw.'