I don't know when they'd become a liability in any case except maybe trying to squeeze through crowded dock areas. (I know I've shoved my H17 through a 12' wide dock openning before.)

They are added weight, but not that much. I honestly don't know why more don't have them. I've read that you can order the Fx-one and the fox with wings, but they wont be class legal I don't believe.