There are 3 bowl coring systems out there. The Oneway, the Woodcut, and the McNaughton. Of the 3, I prefer the McNaughton.
Do you need one? Well as a professional, I do. I save wood and time. The major time saving is on the cores where the bottom or the bowl is already shaped and all you need to do is flatten the bottom and make a finish cut. There isn't a lot of time savings on removing the waste wood. It doesn't take too many sets of cored bowls to pay for the tool. Being a professional is a reason to get the tool, but some times, need has nothing to do with getting a tool.
Horse power and torque are some thing to consider as well. A 1 hp motor is a bit minimal, but it can be done. All of the cutters are 3/8 inch wide, and are scrapers, so if you can take a scraper and remove a shaving that wide, you can core on your lathe. The exception here are the McNaughton mini and micro coring systems which have cutters at 1/4 inch wide on the mini and slightly less on the micro. The micro was desighed specifically for the mini lathes.
Oneway: This is the most costly of the systems, it was around $900 US for the whole set up. It is on a fixed center (pivoting point). It has its own mounting plate, and has 4 blades and a support finger that advances under the blade as you core. The biggest advantage of this system is that it is the most stable for the larger bowls. The down sides to me are the support finger and sharpening. While it provides support, you have to shut off the lathe to advance the finger. On a large bowl, this can be 4 or 5 times. The cutters are also a pain to sharpen. You have to remove them from the blade and hold them up to a grinding wheel. There is a jig available for this. You do a surface grind, not a face grind. A diamond hone/stone will touch it up some if you use the coarsest stone, but you need a grinder. The cutter has a tip which breaks the fiber, and then the sides of it cut away the waste. You don't get shavings. There is some play in the mounting plate to vary the angle you come in from, but not much, and if you are at the outside limits of the plate, the support finger can bind in the cut.
Woodcut: This is a nice little system. The emphasis is on little. The big blade is a 5 inch radius, so you can remove about a 12 inch diameter max core. There are 2 blades, with stellite cutters. You sharpen the face of them, and this is simple. This system mounts in your banjo, and you attach the tailstock to the back of the system. It is also on a fixed center/pivoting point. For me, it isn't big enough, and I never have the tailstock on when turning bowls. There can be some chatter when coring larger bowls and harder woods, but a nice little system.
Finally, the McNaughton. I prefer this system as it is the fastest, and offers the most versatility. You can core plates, bowls and deeper vessels. They have large, standard, mini and micro systems available. I use the standard set about 99% of the time. You don't need the whole set up. I have everything, in part because I demonstrate, and also because I am a tool junkie. The down side to it is that there is a learning curve. It isn't on a pivoting center so you have to guide it. It also tends to drift away from the intended path you are cutting on. You need to learn how to compensate for this. Also, since there isn't a pivot point, you can go through the bottom making lamp shades or funnels. There is a laser pointer available, which I love as it lets me know exactly where I am when coring. Sharpening is simple. The point is diamond shaped and you sharpen the face, not the top. A rough diamond hone does a good job, and I do take mine to the grinder a lot. This is not a tool that you can just pick up and use. You need to have some one mentor you, or there are 2 videos showing its use, one by Mike Mahoney, and the other by me. I believe both are available at the Tool Post over there. I don't really know if they carry all 3 coring systems or not.
robo hippy