I have byrd shelix cutterheads in my 15" planer and 12" jointer. I would never go back to straight knives.
My planer is 11 years old and the jointer is 8. I have not rotated cutters in either machine.
Introduction to Helical Cutter Heads
Four main advantages
Helical cutter heads are also called journal heads or indexable insert cutter heads. What this means on a technical level is that the cutter head employs a more or less foolproof system for cutter placement. When you change cutters, you are virtually guaranteed correct placement of the cutter in the head. Most cutters used for metal working lathes and milling machines employ this type of system, but to woodworkers it’s largely unknown. This is one of four benefits to woodworkers.
The second advantage of indexable inserts is the fact that they are made of carbide. While carbide knives have long been available for straight knife heads, they are not the best choice of knife for straight knife heads. If you happen to hit a staple, nail, or screw there is a strong chance that you will crack the knife, ruining it. Because a crack through the knife can’t be sharpened out, you are forced to buy a new set of knives, which could be several hundred dollars. Indexable inserts are not unbreakable. They will still chip and crack if you hit metal. However, they are inexpensive, with most inserts ranging from $3–6, making a “chipped tooth” much less painful to the wallet. You can also replace just one insert at any given time, so if you happen to chip one in the middle of a job, you can change that one insert and keep going.
The third advantage of helical cutter heads is a noise reduction. Conventional straight knife cutters take one big bite of wood, three or four times per rotation, when the knife contacts the wood. Helical heads have the inserts staggered around the circumference of the head. Because of this, only one or two inserts, which are usually 1/2" to 3/4" in width, are in contact with the material at any time. The result is dramatic. Machine noise can be reduced by as much as 50 percent through the installation of a helical cutter head.
The fourth, and probably most important advantage for woodworkers is the greatly reduced tear-out that these cutter heads produce. While most planers have no problem with straight grained wood, they generally do not produce good results with knots, burls, and figured woods. Helical heads typically produce much smoother finishes on these difficult woods.
And one disadvantage
There is one surprising difference with helical cutter heads over straight-knife machines: Helical cutter heads take more effort to feed. If you were to install a helical cutter in your jointer, you will notice that it takes more effort to push the board through the machine. The reason is simple. Previously, the wood only met with resistance from the spinning knives three or four times per rotation (depending on how many knives your machine has). With a helical cutter head, there is always at least one knife in contact with the wood, thus constant resistance to your push. As a result of this, planers and jointers typically use more horsepower when a helical cutter head is installed.