Personally, I wouldn't do it. GPS tracking won't keep them from getting hit by a car or getting into fights with wild animals or other cats. I don't think I could ever handle allowing any of my cats to roam. There's just too many risks and if something happened, I don't think I could forgive myself.
How much do you play with your cats indoors? Indoor cats, especially very energetic/active ones, need quite a lot of play time to be happy and healthy. Even if you take them outside on a leash, they still need lots of quality indoor play time.
Have you considered trying out a different harness for your cat who doesn't like the harness? Maybe there's another design that would be more comfortable for her.
And how do you know that she doesn't like it? Does she try to struggle out of her harness? If so, she may need more time to get used to the leash and harness indoors before taking her out.
Is it that she doesn't walk on the leash like a dog? From what I understand, most cats will not walk on a leash like a dog. They'll just sort of wander and explore, and you just sort of have to follow them around and let them lead you (while of course keeping them out of dangerous situations).
I'm starting to work on harness/leash training both my kitties so I've been doing some research and talking to some people about the subject. Not trying to say I'm an expert. Far from it. But I'd try to work with your kitty on the leash more before I'd let her roam free, even with GPS tracking.
Jennifer and the kitties, Coda and Caligula