I'm looking to get into a Benz from our Audi Q7, not sure what MBFS teirs/rates are but **bleep** 1.99% is awesome. What credit union?
The lowest I've heard from them is 3.99 in new cars. When I sold cars - this was from customers in the excellent range.
I would honestly just stick with the 1.99 you got that's amazing. (congrats on that by the way) I honestly hardly doubt they could even try to beat it. Unless it was pre-certified which I have heard of the 1.99 in.
You could shop around credit unions, but I feel like you may get a hard pull from the them and be disappointed. Hope that helps and good luck on your new car!