the ball is overrated, when compared to the conventional ones they imply its much harder to manage a normal one, but is all rubbish, as they refer to conventional as having like 4 wheels, however, the two rear wheels move indepently of each other and the front wheel (the spinning bristle roller thing) isn't fixed at all, as its spinning fast so it doesn affect steering the thing anyway as theres no traction
i'm not sure if any of that makes sense, but it does to me, the cheaper ones will still do the job as well, if not better