Keyless entry system

Do any of you guys have any experience with the passive keyless / push button start systems that are all over E-Bay. I see them on there anywhere for $50. to $500.
There are all different kinds out there, mostly from China and I usually stay away from anything made there. But if there is a good one made there maybe.
I am wanting to know if they work good once you have them wired up.
I think it would be kind of cool to be able to just walk up to my car and the doors unlock without having to have keys, just a keyfob in your pocket.
Any info would be great.
Thanks Mike