G'day WW
I haven't used the product that you linked above, but I have for close to 3 decades used a hand held carborundum stone to sharpen & maintain convex edges. In the last 10 years I have exclusively used Fallkniven DC 3 & 4 hand held stones.
IMO, even the greatest wannabe on the 'net, ms (after being told about this) admits that a convex edge can be maintained with a hand held stone.
Heck, he has even used this information to try and convince any one who would listen to him "that the carving ability of a scandi grind" is because it is sharpened with a hand stone that has produced a convex grind.
IMO, pity those who are gullible enough to swallow his marketing crap. :jerkit:
Mick
Big Mike