I do the regular tests (I think they just test me for stuff), but I don't do screening beyond that. I refuse the tests you are talking about. I've heard of women having abortions due to results from those tests, only to find out the baby was actually healthy.
For me, it will make no difference. If baby has Downs or any other syndrome it wouldn't change anything for me (which my oldest has a rare genetic disorder that causes bone marrow failure & cancers, so I can say I know for sure it makes no difference to me...and I have a 1 in 4 chance of having another with it...still won't tempt me to take the tests). I refuse doing amnios as well. The risk of miscarriage is 1 in 200. I know two women (possibly more) who have lost babies to this.
Point being, I guess you should think about what you would do with those results. I know it's nice to know in advance, but if you'll keep the baby no matter what, then there's no harm in waiting until birth.
I don't mean to be telling you something you're not asking for! Just offering my experience in case it helps at all. Choose what feels right for you...and sorry that I can't give more specifics on the test. I'd probably follow the dr's advice about which one to do if you're wanting to do one.