I would maybe add drill across the back corner sides, so if anyone desired to, they could loop a small cord through it for extraction. From the pics, it looks easy enough to remove without a string though. The Cube tip shapers have a hole like this, although they attach a small chain and keyring loop.Here is how it looks in use, from the side and from above.
View attachment 748341
View attachment 748340
It doesn't stick out much.
https://cdn.shopify.com/s/files/1/1062/7500/products/cue_cube_keychain_large.jpg?v=1491246124
I would buy (at least) one too, although it would likely get more use as a pocket marker (APA 8-ball), than for the intended purpose. I would pay more for the brass too, assuming a price difference.