Does a thagomizer can help in  a grapple, giving a edge to grapple or to attack someone while grappling him/her? Or making a attack against a second person while holding the first person grappled?

And Im doing a porcupine concept, can I just take the Thagomizer and say the spike are in facts quills? Since quills can detach and doing the same desavantage as the Signature default (making the quills quality too much too much high I think for his value), I taken the Signature default to illustrate that. So I only have long and hard quills on my porcupine tail but not somewhere else. It is acceptable?