Its confirmed, you cant trust every review you read

The app does provide finer and more incremental volume control. Just look at the negative reviews-- why doesnt it make my iPhone louder? Why doesnt improve my bass? Why? Because the app doesnt promise to do that. It does what it promises to do. Relative to the one reviewer that commented they saw the iphone default volume slider and that this meant it did nothing, thats false. The slider shows whenever the volume changes in any increment.

TechClock about Volume Master - Dial in the sound of your music player with a control booster