The lead isnt attached at the side. It moves around a little as the cat moves. When walking, the lead is at the top of the harness above the cat.
In the photos its at the side because I am sitting down with Elle.
To stop tangling when walking, you hold the leash so the lead stays above the cat. You will get moments when the cat does something to cause the lead to go under their legs, but thats the way cats are. You just have to be on guard really. If the harness is adjusted correctly, then the cat wont be able to put their legs through (or at least I hope not).
Elle took to the leash from day one, but some cats wont like it. In those cases I guess take it slow. Put the harness on and let them get used to it at home for a while. The harness should be worn as Elle is wearing it or the cat may escape.