if I was to get only one, which one is more useful.

- I plan to get the edge bevel tool.
- both stone are about $9 - $10

It all depends on what you hope to use them for. A gummi stone is
something you apply with just your hands, it doesn't work with a bevel tool,
and it is only used for de-burring edges.

If my "hard pocket stone" you mean a diamond stone, then it *might* work
with a bevel tool if it is file-shaped. Diamond stones are good for
deburring and polishing edges, and also for handling situations where your
edges get case-hardened by an impact and become harder than a regular file.
Using a bevel tool with a diamond stone is only useful for *maintaining* a
beveled edge, you don't remove enough steel to *create* a beveled edge. For
that you need a regular file.

Mike T