Display Widgets is a super intuitive, comfortably wysiwyg solution for widget filtering and logic.
First, you select whether your filter criteria should be applied to display or to hide things. After that, you just check the pages you want your filter criteria to be applied to. No need to write conditional PHP tags, just check your options. Additional fields for Post IDs enable you to display any widget on a by-post level.
The plugin works like a charm out of the box, without any warning even in debug mode. Great plugin, I refer it all the time.