Honestly I prefer the sound of MB Quart's to the Alpine type R's (also 6.5") , not that the type R's aren't good.
I put my tweeters in the kicks in an attempt to maintain an even sound stage and avoid possible phase issues.
With the tweets up high thery're quite far from the woofers, resulting in a slight delay from when the signal gets to your ear between the tweets and the woofers.
Putting the tweeters in the kick panels also keeps the distance between the left tweeter and the right tweeter closer together. So the sound is more centered.
They're also out of the way down there, so they're not noticeable to someone looking from the outside.
My mate's got the tweeters of his Type R's mounted in the factory spots on the dash, where those fake vents are. To me, they sound way too harsh sitting up there and reflecting off the glass. I guess maybe if they were attenuated 3-6db that might take away that problem a little.
I couldn't put my crossovers on that black plastic bit cos it's all taken up with excess cable. That's not a bad idea at all though!