BBLight can also do vibe-and-ring at the same time, and is customizable for how long and how frequent the vibration is, if you care... BBLight also had a few other 'backlight" features.
I have tried Peek-a-boo, but not great success. First, it is not "silent", but like very low volume. Also, you have to take 4 photos at once and through the apps, meaning if you just bring up the camera and shoot, it will still have the shutter sound. Also, since it takes 4 photos in a row, there is no autofocus, so the picture comes out crappy. I also thought that the peek-a-boo site also mention it is not compatible with the auto-focus for certain BB model, and 8900 is one of those.