There are a couple different type's out there. Hyperfax have a teflon insert, some mountain riders will use them and remove the idler wheels for less weight. They usually run about $150-160 a set US. Draw back is you cant use a closed window track with hyperfax unless you install wear buttons in the closed windows.
Another type is the "super slippery hyfax". These are sold though HPE and others for about $80 pair. They are black and made from a harder material then regular hyfax. These can be used with closed window tracks. I have used this type of hyfax before with good results. They last a long time, I'm not so sure I would believe their claims of faster top speeds, but I suppose it could be possable. After running a set through the planer for the grass drags, I can tell you they are indeed made from a harder material.
I'm not sure if the extra cost is worth it, for your average trail rider. However if your looking for every last bit of performance, ie racing, etc, then I think they are worth the money.
Unless it's $260 then yea, that's to much money IMO.