the good : this thing do what it say it will do and sound pretty awesome . you will not use the full volume without do ear damage , unless you already have ear damage . it successfully take the underpowered Razor Maxx output and deliver excellent sound , while improve the range -lrb- bass . -rrb- the Bad : I do not know how they define `` normal use '' , but 10 hour be a pipe dream . I be lucky to get a hour out of it at perhaps half its volume potential . if they make a bigger one that hold a bigger battery , that would actually last 10 hour ; I would pay 5 time the price in a heartbeat ... and probably 10 . that be say ; this thing be still worth every penny they be ask for it , as the price be very fair for what you actually get .