I used volume + free, and then I got the paid version.. def heard a difference with the paid version.. My girlfriend was in the kitchen and said "Did you get your phone to go louder?!" because she was making fun of my phone for being so low (she has an iphone).
What I would suggest is keep a song playing in the background with Volume+ and try "+1, +2, +3 etc until it sounds loud enough." I kept my volume at +8 to be safe, but +10 was better.
I really hated having to pay for something that should be working in the first place. Oh well, it was worth it.