I use play sand from Bunnings, and have never had any issues with it. It gets stirred up enough when I gravel vac that it keeps the gas bubbles under control, and I also have Malaysian trumpet snails, and they like to dig around in it, which also helps.
I didn't think you could use UGF with sand, because it would be too dense to allow waterflow?
I think sand is heaps better than gravel, because with gravel all the poo gets trapped in it, and you can gravel vac forever and it will still be sucking up poo, but with sand it all just sits on top and so it's really easy to remove and then it looks all clean and nice.
Not to mention it's more natural for the fish, because when was the last time you saw gravel at the bottom of a river or lake? Especially for bottom dwelling fish, because most of them spend a lot of time lying on it, so sharp gravel isn't ideal, and a lot of them like to dig around in it too, which they can't do with gravel, so it's stopping them from expressing natural behaviour.