"Small disadvantages for all of the advantages (solid stairs, and extremely easy to use)"
Yes, the solid stairs are solid, hence the name. Extremely easy to use? Well, not as much as the fold out steps that simply fold out, hence the name. No having to adjust, and readjust for different stops like the solid steps.
"All of the advantages", which seem to be...they are solid. They may be solid, but they still stink. They may be fine for people with climbing and balance problems, but for every one else, they stink. JMO of course. :)