I do use a collar around the tool rest post to keep the cutter at center height. One collar does seem to work for all 3 sets of blades. I have found that especially on large bowls that by the time the cutter gets to the bottom, it can be below center. There is some flex in the blade, and the tool rest support, especially when you are hanging out there a ways. This will lead to more chattering, but seldom any catches. I do prefer to be slightly above center when starting the cut. Kind of standard for any tool when working on the inside of a bowl.
As far as differences in the 2 systems, The McNaughton is by far more versatile. You can core plates, standard bowls, and deeper vessels. This is because of the variety of blade shapes there are to work with. With the fixed center Oneway, there is a little play for side to side for going deeper, or shallower, but if you go all the way to either side, there are problems with the support finger binding in the cut. The biggest time difference comes from having to advance the support finger on the Oneway. This means on a bigger bowl that you have to turn off your lathe 4 or more times to advance the support finger. I also don't like sharpening the cutters. You have to take them off the lathe, then hold them up to a grinder. You have to sharpen the top surface because of the point on the front of the cutter. If I was to use this in production, I would make a surface grinder of some sort. A diamond stone just doens't quite cut it.
The McNaughton is faster for me to set up and use, but, there is a learning curve. This is not a tool to try to learn all by yourself. The instructions that come with it aren't very good, and you need some one to show you how, or get a DVD. Mike has one, and I have one as well with a slightly different approach.
robo hippy