What is the difference between these air ducts?
We have a portable AC as well. Since the original pipe was too short, the only way to run the exhaust was to swap it out for the piping you have pictured at the top. It stretched over the original terminations at the AC unit and the window just fine. I held in place with duct tape. The pipe I used was 15' long compared to the original 6' pipe like you have. I was concerned about an increase in static pressure and how the unit would perform, but it did work very well on cooling the part of the house we needed with no issue.

"Threading" it on was not an issue, it was just pulled straight on and brought a wire or 2 over the nibs that acted as threads for the original pipe.