The big problem with the Lightshpere is that you can't direct the light. This is an extremely inefficient design, because you send light in every direction whether you want to or not. This means your flash may have to work that much harder to light the irrelevant void behind you. This unnecessarily drains your batteries and increases your recycle times. Not good.
But more importantly, you sacrifice creative control! The omni directional Lightsphere will bounce off of EVERY surface whether you want it to or not! But a good photographer wants to control and direct his light. So while the Lightsphere might me a useful crutch for an amateur who doesn't understand more advanced lighting techniques, a more talented pro will prefer a well placed bounce or directional fill over a general shotgun blast of light everywhere. Once again, inefficient and void of creative control.
Also, some believe that the Lightshpere helps outdoors. To significantly increase the quality of your light, you must significantly increase the size of your light source relative to the size of your subject. I use 19" softboxes on my off camera strobes and can barely tell the difference between them and direct flash. This is because my subjects (and yours) and 6 feet tall, and the difference in the size of your light source changing a few inches is insignificant relative to the size of your subject. This is why studios use softboxes that are 4 feet wide. Now there's an improvement of your light source.
So, save your money and learn how to bounce, either direct or with a creative tool like the FlipIt, or a Better Bounce card. Your photos, your clients, and the left side of your brain will thank you for it.