I use this in my tanks. I like the natural look of it and my fish being red and purple/red/bluish it really looks great with them.
If your airstone is one of those that has the plastic on the bottom you could use aquarium sealant to glue it to a rock or something. I used to anchor mine underneath decor like my skull before I got gravel.
It's all a matter of preferences. Gravel requires a little extra work in cleaning but you'd need to siphon out waste regardless if you have substrate or not. Go with what you like looking at! No matter what anyone says you are the one who has to look at your tank :3