Your myEcho purchase is tied to your AppleID. The Windows Companion App has no DRM or licensing and you can install it on as many machines as you'd like. If you have lots of iOS devices and lots of Windows machines, though, be sure you're aware of which device is paired with which Windows machine (and know where you're running the Companion App) otherwise your spouse may be shocked to find text appearing in his Word Document at home while you're at work!