I don't buy them generally however I made one the other day!
I had some tapioca large pearls which I had left over from a dessert and so i put some watermelon in the processor and poured it over my cooked tapioca, and then did the same with a kiwi fruit.
It was not an ordinary slushie but was lovely - perhaps a bit like boba or bubble tea without the tea and the sugar!
Though the tapioca took me several attempts to make as it all went to mush when I first soaked it as the packet said.
I find slushies "go to my head" like ice cream sometimes does, but I have not actually bought one from a machine like the photo for many, many years.
I had my first one two days ago and found it terribly sweet. No wonder the kids are addicted to them. My teenage grandkids tell me that you pinch your nose as you slurp to avoid brain freeze. However, I drink slowly so avoid that.