These babies can be had for under £30, which is very cheap in the world of car audio. But don't let this fool you; they are brilliant. I coupled mine up to a Sony Bluetooth head unit, I had 2 of these speakers in the back of a Fiat Seicento, and a smaller, 4"ish pair in the front (other than size, they were identical to these). I decided upon Kenwood because they were much cheaper than the Sony equivalents, plus they did the speaker system for the McLaren F1, and that's the greatest car ever made.
First things first, these are not going to compete with Bose, B&W and B&O, who all make factory installed solutions for higher end cars, but we're not talking a £20,000 BMW here, rather a £1000 Fiat. Installation was a doddle, the bigger speakers simply slotted into the parcel shelf, and were the same size as the terrible factory installed Fiat ones. The fronts took a little more effort, some of the metal 'ears' on the outside of the speaker had to be bent so they would fit in the holes in the dash (I wasn't cutting up the dash of my Fiat). But they got in, and stayed in place perfectly until I removed them and sold the car.

I fiddled around for hours with the EQ and fade settings on the head unit for the best sound, but I eventually hit the sweet spot. The mids and highs are more audible on the 4" model than this larger one; where the bass is more prevalent. In fact, there was enough bass to negate the need for a separate subwoofer in the boot, which was handy as the car had very little bootspace at all. While the bass on the bigger ones was great, the mids and highs seemed to get lost somewhere, but that's where the smaller front ones came in. They have far less bass, not quite to the point of non existent, but they lack on bass. However the mids and highs are pretty good on them, so the two sizes of speaker complement each other very well. Please don't think however, that they will instantly make your Saxo have a Bang & Olufsen rivalling stereo; they won't. This isn't so much down to the speakers themselves, more the effectiveness of the sound deadening in the car. Poorer sound insulation means a poorer quality, but I have no doubt that these would be much better in a car that had more sound deadening than my rusty old Fiat.

So, if you're a fan of better quality sound, but have a smaller budget and don't have a BMW with a high end stereo in it, then get these, hook them up to a decent head unit and there you go, much improved quality over the factory fitted option. And at £30 a pair, reasonably priced too. If you want Bose quality, go pay Bose prices.