I've been using the Ringmaster for years, and the trick is to get the segments thick enough that you can produce at least a slight curve on the outside of the bowl so everything isn't just straight lines.
It's a machine that cuts slanted concentric rings from a board that you stack, glue together and turn to make a "bowl from a board" - without a bandsaw. More info on their website: http://www.ringmastertool.com/
Do you mean a Bowl Saver? If so, these are completely different animals; the Bowl Saver cores out the center of a bowl blank instead of wasting it, the Ringmaster cuts concentric circles from a 3/4" board that be combined to make a bowl.
I do believe that anyone with a lathe can already do the same thing with a little care and sharp tools.
BTW, for the money I would rather have a lathe as it can do much, much more than just cut rings and such ... hummmmm, is that all this machine can cut - rings!
In that case, the only thing the RingMaster does is cut the rings faster and you don't have to glue the pieces together. No, it really isn't worth $600 just to do that. No matter how you cut it, they're all still in the "boards from a bowl" family.
As for cutting the rings on the lathe with a parting tool, many people do that. The only thing the RingMaster does different is cut from both sides of the board so you don't get tearout on the rings. Again, not worth $600 just for that.
To be fair, the RingMaster without the motor to attach to your lathe is only $400.
All seriousness aside, the only reason I have one is that I picked it up used for $25. If I had to pay full cost for a new one I would use the parting tool method instead. The only "difficult" part is getting the angle right so that the rings stack properly, with the inside diameter of the larger (top) ring matching the outside diameter of the smaller (lower) ring.
thank you for the nice replies. I don't know if I would pay for a new one seeing that bowls are just something I do extra. along with everything else. I'm buying this one used if I buy it. It is nice it is just like that commercial set and forget it (far as cutting that is Ha Ha) I like it so far.