That's a great question! You can use the SlingPlayer application for more than one device depending on the devices. You can purchase the SlingPlayer application for the iPhone and load it on the iPod and the iPad. With the Kindle Fire, it would need to be purchased separately due to it is sold through a different platform. (i.e. iPhone/iPad/iPod are all through iTunes, and Kindle Fire apps go through amazon.com). Below is also a link that explains loading the SlingPlayer application on more than one device:
Hope this helps!
The Sling Moderation Team
You can use the iPhone app on the iPad, and the iPod touch. So that saves you $30! But since the Kindle Fire doesn't use the app store by apple you have to download the app from amazon so that is just another 15$. Just a warning about the iPad you will have to make sure it says (iPhone) next to it or it will charge you again, and it streches the app on the iPad so it might look a little bit fuzzy