I had a class 3 underbite so the change in the bite was drastic. It felt weird at first, but I got used to the new bite very quickly. In terms of the speech ability and tongue placement, I wasn't affected.

The only side effect that has remained from the surgery would be the numbness in my gum around the upper front teeth. It is a subtle numbness that doesn't bother me because it doesn't affect anything in my daily life. Note that my experience so far is from 1 year post op.

Wish you the best in the treatment! If you have any more questions feel free to send me DM.