K.B.
IMO-- It's not always important that you click with the parent...It IS important that the kids click with each other. If you do not approve of something with the parent, you just need to decide if it's something minor, or major enough that you do not want to leave your child alone with them...maybe a differing parenting style or something....
The MOST important thing is if the kids click...you do not have to be friends with all the parents of your kid's friends....because that will never happen. But it's an added bonus if not only YOUR child made a new friend, but you did too...
Enjoy that your child is coming out of his shell and enjoy the friendship that your child has with this other child.
And please do not stop a blooming friendship for your child because you are afraid YOU may not get along with the parent...to be honest, that is selfish. It's not about you, it's about him.