...You can send log messages to the console, view SQL Querys, memory usage, list of user and server vars, files included, automatic detection of ajax request (like FireBug)... etc.
Also PBL can send emails to the admin when a sql query fail or the app are using more memory or time that allowed. You can configure this.
PBL don't have dependencies. It automatically generate all the HTML, JS and CSS code for show the console on your browser.