Certainly, putting this URL on a page for other people to read is a very bad idea -- like tossing your (physical) wallet out your car window.

The intent of the URL is that you should bookmark it and otherwise keep it private.

Unless you know of some way for an attacker to get at the browser's bookmark list (which I'd be interested to know about; I'm certainly not enough of an expert to be sure that no such attack exists) then this seems fairly secure.