Rich,
O rings are made from Neoprene. Which lasts longer?...depends. Some people may prefer to replace the string more often and it can take a little time to get the hang of replacing. With O ring its just so much easier. O rings are easier to replace and probably last as long. Some have spoke of O ring failure but I have never had that happen. I have one that I use mostly for lighting my cigs and for the last 4 months or so it has created coals tousands of times with the original O ring and no signs of wear. In fact, I am working style in my head that has both on one rod so chose is easier.
Opps,
There was some Chaga left over in the cup when I tested it out. Its harder to push down because of the compression. Sometimes harder, as with all string models, if it has sat idle awhile and needs some serious lubricating. Glad to hear you got your model from Jeff.