Putting up posters in hard to reach places
If you're only going to ever need it for your own staircase investing in such an expensive adjustable platform may not be warranted. 

you can probably build your own from some some 6x2 lumber 

cut pieces to make the basic shape of the ladder ledge and fasten the parts together with structural screws, fit rubber feet or a layer of rubber anti-slip floor surface 
to the underside,