A lack of legs on the dress form means the bustle tips forward at the bottom. Legs and the inner panel stop this tilting on a person.
This bustle and train supporter was not difficult to make as the instructions were clear and well illustrated. I did however find that I needed to change one thing and that was due to fit and could be because I am shorter than average - it was not a big deal or a problem. There is internal or hidden structure to this bustle (and to most others). This internal structure consists of simple panels that rest across the bum and across the calves.
I found the upper panel, the one that rests against the bum, to be too large. Even when it is laced tight as in the photo it did not pull the bustle shape to where it would suit me... or my taste. I have narrow hips and this could be the issue. Were I to make this for myself again I would scale down the top panels. I also found that I needed to move the lower panel that is at calf level. The pattern instructions indicated that this panel be attached further to the inner curve of the bustle but I found it bounced off my calves too much when I walked -this may not have happened if I had a skirt over it to add weight. I moved the panel to the front edge of the bustle and preferred the balance this gave.
These comments are not to say there are problems with the pattern. You should probably follow the instructions given with the pattern especially if you are wearing a skirt with a train. I've made these comments so you understand that you may need to make some minor alterations to suit your purposes, and that altering this pattern was quite easy.