Hey Danny, welcome back!
I can remember the first few times I saw the effect in a movie and thought that that was super cool. The subject/character would disperse in tiny fragments or balls and would wisp away to nothing!
I've always been a fan of dispersions but very few get it right using Photoshop. You have come the closest I've seen in awhile! If I did offer a suggestion, it would be to add the wispy trails of the tiny fragments. I commend you also on creating this effect on a dark background..........you almost never see anyone try that.
The effect in the hand is fantastic! It seems a little flat to me meaning the effect does not have much dimension if that makes any sense.
All in all you have done stupendous job here, thanks for sharing!