You can freehand but Hannes also sells a jig that kind of replicates it. I have this gouge and don’t use it often but on the occasion when I want it at least I have it. I have several of his tools and do use them often. I believe Doug T made the tools to Hannes specifications. The handles are awesome!That flute is awfully short and there is no flat milled on the shaft. What sharpening jig would be effective without a flat to register against as the flute gets shorter? Would freehand sharpening be necessary?
I also have that tool and the addition of jig to use it with Hannes' sharpening system. For bowls it removes lots of wood fast!