I like them and think they make a difference. The problem is, they are easy to blow and it's hard to get good sound quality from such a small speaker. Most long drives in my Miata are to autocrosses and I listen to Podcasts, so I do not need quality sound for music. I can hear the Podcasts better with them than without.
Mine are the Millennium S. There is another thread on here where a guy used speakers from a cheap surround sound system and liked the results.