I knew a guy years ago who was making whittling/carving knives out of hacksaw blades. Not sure how he put handles on them, probably just a split dowel sandwich with tape wrapped around it... but man he got those things sharp!
Yes, gotta slow down I've found and do little bits at a time so the heat doesn't build up. I assume stainless is denser and probably heats up faster and holds heat longer than brass. I have scorched the wood around pins ( and called it a "special effect") and melted the innards out of a mosaic...
I notice that the style of rasp he is using looks awkward to hold onto on the front end. I think the one Rockler (more $ of course) sells and one of those referred to earlier on amazon have a detachable raised handle that helps make even pressure strokes.
The ones I've seen at Rockler look like a spiderweb of hacksaw blades on edge. The one you show appears to be reversible with two different degrees of raspiness. I think they can take material off fairly quickly, but don't know how rough a surface they leave.
That's really cool looking! Am I understanding this right... Is the front portion/guard going to be damascus and flow with the pattern in the blade? That looks tricky. What material are you thinking for the scales?