david weaver
Even india stones are probably hard on a diamond hone. SiC, definitely. I think very coarse stones for anything other than bevel work are generally a pipe dream (at least considering them to be "good" for that kind of work).

Kanaban with diamonds is good (and very cheap), but even the kanaban will need to be flattened after a while, which is a pain in the rear. PSA paper on glass is much faster for nearly all things, but not quite as cheap in the long run (the time tradeoff is worth it, though).

The only really good coarse stone is the crystolon type or an equivalent type for water, and they don't like to stay flat - and flattening them tends to grade them and load them.

I have bought a lot of coarse stones, but wouldn't again buy anything other than a medium crystolon below the shapton 1000 grit level.

I guess an india stone is technically more coarse than that, but they are only slightly faster than a stone of that type once they've settled in, and you can keep them flat by using them properly. There is no absolute need that I can think of for a flat stone in the shop. A skilled user can maintain the back of an iron or chisel on the end of a swayed stone, even though it may not be ideal.