My family is currently setting up my new tank for my Betta while I'm away at college and my mom decided she just had to have some of these (but in blue) to put in the tank on top of the sand. I don't know if would be easier to clean than gravel but you're right it certainly looks that way. At the very least I don't think it could actually harm a betta by having them in there.
Gravel accents are easier to clean, especially during 100% (you can put them in a strainer.
I use plain ol' gravel though. I use a strainer for them, but at much smaller handfuls.
It just depends on what you prefer looking at I think.