I tried it but didnt like it much. Its easy enough to use the default ipod on the switcher. I use activator to switch forwards and backwards. That alone is a great reason to jailbreak since I use my phone for music everyday. I have zephyr so I can swipe up to show my app switcher, than slide to the side for the ipod controls. I dont have spotify so I cant see if the mini player works with it. I assume it does since its a simple media controller.
**I should note I keep all my apps on one page for easy access** Using the mini player was redundant since the ipod controls are already built in. If you are considering jailbreaking for mini player, jailbreak for activator instead. So ridiculous that you have to perform multiple button presses by default to simply switch to the next song. Activator allows me to do this while my phone it locked with one button. I hold volume up to switch to next. Volume down to go to previous.