Since they are man made materials, quality control during manufacturing insures the quality of the final product. The latest synthetic materials are tougher than cork, made of closed cell material that won't absorb water, and is UV resistant. This characteristic makes it very nice when it comes to assembling and gluing your handle. If the blank is larger in diameter than the I.D. of the handle piece your are mounting, it will expand to fit the blank. There are limits of course, but fitting cork requires more precise preparation than synthetics.
Synthetics are generally less expensive than cork, and is available in a rainbow of colors.
Handles can be made to match the threadwork on your rod. Wet synthetic often feels cold and slippery. Yes, I said cork can be slippery when wet too, but if it's a matter of contamination, you can fix it with a little steel wool. To be fair, this is one of my biggest biases against man made materials, and was formed for the most part, when I was younger and materials of a lesser quality were available than what is today. According to information that I've read recently, these problems are supposed to be a thing of the past.