Advice: be patient, use the various techniques to get your cat acclimated that are listed on the site.

Ultimately, how cats deal with being harnessed even after being acclimated is extremely individual personality-dependent. I've seen some happily walk like dogs. Mine don't particularly want to walk alongside people and very quickly want to go off under plants or other places where they can hide and stalk, and where people can't easily go. We take them out for as long as both they and we can stand, and don't jerk them around.

The Kitty Holster type harness is significantly less escape-prone than say the PetSafe style of nylon straps, and probably less uncomfortable as well.