I have been istalling car audio for years and these speakers are the best bang for the buck. Now 95% of my installs consist of their speakers, subs, and amps. They are very smooth sounding. If you can afford the M6 series go for it. They are better than the focals that you pay twice as much for.
The tweets sounded pretty harsh out of the box. I was thankful to have the attenuation option for the tweets on the crossovers. Even with the Attenuation on, the tweets were harsh. I about pulled them and went with another component set, but I kept them in for a while and was pleasantly surprised to hear the tweets mellow considerably over time. They still lack the midbass punch, but are not too bad for 5.25. All in all, a pretty sound bargain for the money. I do find that they like to be driven pretty hot. When you drive them hot (I am feeding them 150 watts), the midrange opens up a bit and they compete fairly well with the tweets. However, it is a balancing act to find the perfect combination, since the tweets apparently handle far less wattage than the mids, and the tweets begin to break up as you feed them more power.