I just wanted to see his response. I don't know if you would call them DIY tweeters, they're just tweeters, you just need to get the proper crossover if going passive, or using for home. Don't have to worry as much when going active.
Several of the tweeters that come in component sets are actually really good. I like Crystal Mobile Sound tweeters that come with one of their sets. The Zapco tweeters from their CK 16.2 set are phenomenal as well. But I do agree, there are many tweeters on madisound that are probably cheaper to buy than buying an entire component set just for the tweeter. Alpine (Vifa) XT19's are awesome tweeters. I had ordered some for 40 bucks but they ran out of stock and discontinued them on some other site since madisound didnt have them.
A good place to check out tweeters is
http://www.zaphaudio.com and look for the Tweeter Mish Mash link. The comparison of the mids is also great tool.