I prefer to use a ladder I am very unlikely to fall off of over a tall step ladder with my 20" f/5.....Its a $150 4 step (total) with wide steps little giant jumbo step with non-skid rubber on the steps, has a handle/lean bar/eyepiece holder hip high above the top step and the top is extra wide.....I guess one could call it a "serious" ladder in a sense but certainly not height/size wise unlike the tall step ladder you showed......
A photo would be helpful. Railings to lean against are really nice and transform the viewing experience. Just missing the bottom step step on the way down and taking a tumble is enough of a fall to be seriously hurt. Having a railing to hold onto, lean against, shallow step angles, wide steps.
A scope like this requires a real ladder. A scope with a 76inch focal length might get by with a short stool and one can get by without the stool for much of the sky. For my 22 inch which has a slightly shorter focal length than a 20 inch F/5 and a very similar eyepiece height, I can view standing up to 40 degrees elevation. Beyond that it requires a ladder. I am 6 ft. So with a scope like this, much of the viewing is done with a ladder.
The gain of a 20 inch over a 16 inch is slightly less than 0.5 magnitudes, significant but not so different. A 16 F/4.5 inch is much easier to setup, transport and does not require a ladder. A shorter observer may require a single step stool. An 18 inch F/4 is bigger, gives up about 0.22 magnitudes to a 20 inch but again does not require a ladder, etc.
What I see is that with the arrival of the Paracorr 2 and sub F/4 scopes, these older scopes have become relatively inexpensive. As I said, I don't see $5000 as a steal, it's a reasonable price and a good scope. If you haven't spent much time with a 20 inch F/5, it's good to consider just how big it is and how much hassle a ladder is.