Those test's are meant to be used a screening tool to see if someone should be looked at as possibly having Autism/Aspergers. I think it is worth it if it is going to help you in some way. For me it is helping me feel better about my past (I didn't do this to myself) and also my therapist and doctor to understand how I really am.

I see you are in the UK, so you can be diagnosed for free, but I know some autistics there who are unable to get insurance due to their diagnosis.