This app is interesting however, users are signing up for this with the idea that no one among their friends get to know about it. Unfortunately, facebook enthusiastically shows everyone using various apps.

Not sure if facebook has a privacy setting to prevent others from knowing the apps I use but if they do then the developers of this app should inform this to their users.

If facebook does not have a way for me to hide from my friends the apps I use then IMO, facebook should have this option.