I'm kind of impressed at how those bits look pretty much identical to what you'd get today, and from the looks of it, they would fit in a modern Dremel rotary tool.
They definitely were worth it over “acoustic” erasers, but cost something like $70. The few times I got to use one spoiled me.
This is a reminder of so many things: Like chip and board "tape out" being done with actual tape on velum...