Congrats!
I received mine about 2 weeks ago. While I haven't practiced with them, I do have three rounds with them, and here is what I've noticed.

Definitely more spin/stopping power.

They feel heavier than the SM8. I assume that is a result of the CG being moved higher/back, and more tungsten (if there is more tungsten).

They feel more stable to me, and easier to square up.

Easier to get airborne (for me), but definitely flighted lower, which I love.

Easier out of bunkers (height, and spin).

I have the same lofts as my SM8's, but seem to be hitting them all 5-10 yards further (50.12F, 54.10S, 58.12D)
Off to my lesson this afternoon. I'll be gapping them with Trackman.

That's my assessment. I'll be curious to hear what others think.

I have the SM9 58.14K Grind. My other wedges are SM8's. I know that the SM9's are cast from the same carbon steel as the SM8's, but the SM9 feels softer. I love the SM9!

SM9, isn't it just amazing? Enjoy hitting them every time.