I have generic bristles in my Sanitaire brushroll. The orange and blue ones were toast when I got it, so the generic orange and black ones have been working great since I replaced them. The orange/blue ones were a lot stiffer though....one day I will replace it with the right thing.
They DO make a metal fan for the Sanitaires. I have one in mine. There is absolutely no benefit over the plastic long-blade fan though. The geometry and dimensions are exactly the same for the long blade lexan fan and the metal fan. If this metal fan ever goes boom and doesn't destroy the vacuum in the process, I'll replace it with a lexan since they're cheaper and easier to obtain. The metal fan does make the vacuum a LOT louder though.....it gets a whiney overtone to it.
I have a metal fan in both my Heritage II Legend and the Generation 3. The Heritage II didn't see much improvement over it's stock Lexan fan, but the Generation 3 saw a tremendous improvement over the Kevlar fan it had in it. I wish Kirby would release the old style Lexan fans for the older Kirbys so they could retain their power when the fan is replaced. The Kevlar fan just doesn't cut the mustard in the older style machines due to the shape of the fan housing. They're not designed for the tapered blades.
I've thought about redesigning a brushroll for a Kirby, but I'm entirely too lazy, and besides......if I want something with a good brushroll, I just reach for one of my Hoovers or the Sanitaire! It really is that easy....... Boy I'm lazy.....