Hmm... yeah, after about a half hour clicking the buttons, I don't think that I'll use your app more then once.
It really is a nice way to cull my followers. I'm trying really hard to keep my Twitter account topical and interesting. However, spending the time to go through each and every user more then once doesn't sound like a lot of fun.
1) The Twitter TOS does sort of prohibit this. We know this empirically because some apps that have done this before have been cut-off by Twitter.
2) It would not be scalable to users with huge numbers of friends and also it would take a much longer time to load and sort.