Well I would guess that depends on your vehicle. We have had this X for 2 years now and after all the initial preventative maintenance I have done (valve cover gasket, OFHG, Vanos rebuild etc. etc.) I look under the car there is very little leakage anywhere and the truck performs like new. So for me investing $550 and replacing all those parts it was a no brainer. Plus they are all guaranteed for life.
I have used a remanufactured shaft from Cardone when I had my 330xi that I had purchased from Napa it was also warranted for life. I did have to replace it once due to a torn boot. I do not know the cost of the Cardone shaft but for $256 and lifetime guarantee from FCP it might very well be worth a look.