I agree with the other posts that spiral-wrap flu-flus slow down faster. But if you only do a single spiral-wrap feather per arrow, they don't slow down quite as fast, and it's about the cheapest flu-flu arrow you can make (only takes 1 full-length spiral-wrap feather).
The last bag of 100 spiral-wrap feathers I bought from 3 Rivers I think was around $25. Unless you find some crazy deal, I don't think you can get regular full-length feathers that cheap. It only takes 1 or 2 spiral-wrap feathers per arrow, depending on whether you do single or double spiral-wrap.
If you're doing regular 4-fletch flu-flus, it will take 2 (at minimum) full-length feathers; 6-fletch will probably take 3 full-length feathers.
I like both types of flu-flus. I think regular-fletch flu-flus probably fly a little better, but you can make single-wrap spiral flu-flus cheaper.