It is not a matter of whether a clay tile lined chimney vs a SS liner is better. Its the application. There is nothing wrong with a clay tile lined masonry chimney but when used with a wood stove, especially an insert dumping into it, it just isn't the best situation. A free standing stove with stove pipe into a clay lined masonry chimney may be just fine. Just depends on the application and the individual setup. Listen to the chimney sweep. He is looking at your specific setup and is recommending a liner. So you probably need one