Riccia flutans is fine as a floating plant providing you don't have something like a spraybar from your filter creating a torrent on the surface of your water. It grows in whorls that can be easily broken up by too much surface disturbance.
It will tolerate a fair amount of disturbance providing it has adequate light to make it grow compact, if it grows thin and stringy from lack of light, it will break up quickly and make an horrendous mess in your tank, especially when it looses colour and starts floating around your tank at all water levels.