I bought Preview 1 last time ( which isn’t in the three pics shown at this time – 4 previews, 3pics?) Anyway it is kinda like 3 steps, no curved pieces, tubes. I have a 20 pounder and don’t think she can fit on some of the other creative seating styles. The top seat/level, is a bit small for her.
As far as sturdiness – very sturdy. I purchased several of these and have moved them to various rooms/windows, carried it up and down stairs, and had a BIG cat use it. No tipping issues. It is holding up very well.
It came shipped with no assembly required - all one piece.
I am happy with the construction, just wish the top seat was larger.