Personally I'm set up to switch between such an arrangement (fountek ribbon + cheapo woofer line) and a true array (cheapo tweeter line + cheapo woofer line) . My ribbon is attached to the side of the speaker .

The disadvantages of the single tweeter are
1. the image and soundstage change somewhat from the seating vs standing position. For this reason, I usually leave the cheap tweeter switched in and the ribbon switched off for casual listening, internet radio etc ... and occasionally I sometimes switch to the ribbon when I'm critically listening to high quality recordings, or those with well resolved high frequency content .

2. if your single tweeter is not efficient enough ($$), it can easily be overpowered by the woofer line . Also, the single tweeter will roll off earlier compared to a line of tweeters .
3. make sure your single tweeter can handle the lower crossover point

The advantages of the single tweeter are
1. potentially cheaper than a line of high quality tweeters.
2. much easier to implement
3. you don't have to worry about getting the tweeter flanges as close as possible (since you only have one), risking roll off on the high end.

If your cache of raw drivers satisfy these requirements, try the WWW...T...WWW approach .It's not theoretically correct, but that doesn't mean it will necessarily sound bad . Make sure the tweeter is somewhere near listening height .