I got one of these this year for my 2 year old daughter - it is like elmo in a front-carrier with the strap on the back. Here are my thoughts...
1. Yes, it is like a leash - she even calls hers a leash even though I've always called it a harness to her. We put dogs on leashes to keep them safe - period. Same is true for children. I don't have a problem with that. After reading other responses I would add that just because we do something for our child that we do for an animal or pet is not always a negative - afterall, I feed my dog and I feed my daughter - doesn't mean they're both equal in my eyes.
2. She liked hers the first few times and then began to hate it. Now I VERY consistently offer her a choice whenever we get out of the car somewhere public - harness, stroller (or sometimes shopping cart if that is an option). She chooses, and then HAS to stick with that choice.
3. I've never felt like I got rude looks, but others say that they do. Personally I think it's a matter of perspective. I've had several people come up and say it seems like a great idea, and I get some looks that I consider "quizzical" in which I think they're trying to figure out what I'm doing. I don't assume they're being judgmental, but some parents probably figure that's what those looks mean. Either way, I don't really care what other people think.
4. After reading other responses - people who think that it is lazy parenting probably have an easier child. Children come in all shapes, sizes and temperments. Parents all come with different skill sets. Using a harness doesn't mean the parents simply don't try to teach their child to behave, and it doesn't mean the parent is lazy and wants an "easy out". I can't speak for all parents, but using myself as an example - I have a very well-mannered child and I do teach her how to behave. I have absolutely no interest in taking the easy way out. But there are times that I deem it safest and for everyone's best interest to use a harness. And I don't need to explain those reasons to anyone because no one else will fully know and understand my situation without having lived it. Just as I'll never know and understand theirs. I could argue that it's lazy parenting to stick your kid in a stroller and not let them get exercise. Or to make them hold your hand everywhere without a little more room to roam free. Or I could say that it's simply unsafe to let your child wander about without a harness or holding your hand. See - you can complain about each and every option. I wish I could make others less judgmental, but I can't. All I can control is myself, so I do what works for me and choose to remain judgment-free about the choices that other parents make.