I had a slightly earlier version of that 8" Grizzly jointer (no mobile base) with the helical head, and I was very happy with it. I used it for several years without any problems, and the only reason I sold it was I got a pretty good deal on an Invicta 12" jointer. I then spent almost as much as the jointer cost for a Byrd head for it, which will be installed this summer. I also put helical heads in my two PM 8" jointers at school, and the 12" PM thickness planer. As far as I am concerned, straight knives in jointers and planers are as obsolete as steel blades in table saws or HSS router bits. (But steel knives in shaper heads are another story.)