This is a personal and not a medical professional opinion. And since I'm retired I don't offer medical opinions anyway.
As much as I like to support medical research, I wouldn't let someone do a spinal tap on me for purely research purposes. But then I'm kind of a wuss when I'm at the sharp end of a needle so maybe you shouldn't listen to me.
Interviews - sure, questionnaires - sure, non invasive tests - sure, but invasive procedures - anything beyond a simple blood test, and I'm out.
If I was seriously considering agreeing to the procedure, the questions I would ask are - "Is there any benefit to me? If yes, what is that benefit?" And go from there.