I know the cuffs are made out of seastone but they are overall very think in proportion to a bladed weapon. I was more going on the line of that it would be too hard to shape it into a thin piece and then also sharpen it to make a cutting edge.
If they can make Jutte's out of seastone shows they are able to shape it into circular objects easily which would explain the bolts etc. in the cuffs and don't they even line some marine ships hulls with it so they can cross the calm belt? or was that just an anime thing?
Overall I perceive seastone to be like clay/ terracotta just MUCH stronger. it can be shaped into interesting/ useful shapes but not into something such as a blade.
nope its not just anime thing. It was in the manga at Water 7, Coby told Luffy how he got to Grand Line without going over the Reverse mountain.