With 6*9 you have the same problem as with any coaxial speaker, but because of the increased surface area of the cone of the 6*9 it has a greater affect.
Because the tweeter(s) sit in the center above the cone, when you starting trying to output decent volume, then the air movement from the cone pushes the tweeters around and in severe cases does blow them.
You get the same affect with a big sub in the boot with speakers in the shelf.
With a component speaker you can adjust the height and aim of the tweeters as they are seperate, allowing for superior sound staging. And as they are seperate and you'd have the 6.5" driver down below and tweeters on the dash, they won't get pushed around.
That is superb quality for little cash, especially as far as components go. TBH a good set of front components run from a decent amp, and a half decent sub and amp will be FAR superior than sub and 6*9s but I can get around 20% discount on Infinity