it does work, here is instructions: http://www.idownloadblog.com/2015/07/14/watchdog-app-backgrounder-ios-8-tweak/
it was a bit confusing at first but when you open the Switcher and you see ur apps Tap on the icon under the opened APP Within the switcher and then a colour dot will appear on it and within ur Springboard or folder where ever ur app is the dot will also show there.. just be sure to tap again when ur not using the app coz it will kill ur battery fast..
Note: even if you quit the app from app switcher the app will still run as long it has that red dot on the icon of the app. so if you have closed out of many apps without untapping the backgrounder function your battery will die pretty quick.