I've got the Pro-forme tool , with the heavier handle. havent used it much, but but done a couple of hollow forms and really liked it. Getting the position of the brass cover was a bit of trial and error...too deep and the tool will twist and dig...shallow cuts seems to be the way to go.
I sharpen mine freehand with a trend diamond card, a couple of strokes with the fine side has been ok up to now. first time I sharpened it made a big difference...I was putting it off as it looked awkward but it made all the difference...