If you can and want to claim a Steam key, enjoy! Itch isn't going to take your game away. But since the OP and several others have complained about not being able to install the game, I'm guessing they don't use Steam. My answer was for them.
Viewing post in Can't install Bunny Bash
I'm afraid that's hard to say now. You really ought to contact the developer. Their Twitter account looks abandoned, or at least dormant, but they have a site and an e-mail address. And they seem to be known as the current maintainer of the Vulture GUI for Nethack. Thought it was a mistake at first, but it looks legit.