If I go with poker chips there is no indenting to put the private key. That's why I think it would be better to just print a nice design
You are of course right about the indent and that's something that, if the design is of a high enough standard and the chips of good quality I think would be acceptable. The alternate view would be to get them "routed" so a small indent is created there, but as with all things, add a process and you're adding cost. Lots to research and time to spend...
Numbering was also another issue with the choice being "on holo" etching or "on chip", but then materials plays its part in that drama too....
As a result of our previous chat I did actually follow up with some manufacturers and holo makers.... it was an interesting pursuit and one that may yet yield dividends.
Viz