Mein Deutsch ist nich so gut, also Ich muss in Englisch antworten.
The main use for this is to find quest items or the same type of items easily. I hate when a quest says "use the magic crystal" and you don't know what it looks like in the bag. This way you type "magic crystal" and it shows you. Also good if you don't want to flip through all your tabs (I rent all 6) to find where a looted item went.
I can't say whether or not it is compatible with any other bag addon. It's up to the author of those addons really. It would be a tremendous amount of work to add support for every bag addon out there...
I looked up fliebag though, and it might be okay. As long as the author kept the normal naming of the bag icons and tabs, the mod should work with it.