If you are determined to repurpose an old device, these are the common community-suggested workarounds:
: Historically, IPA files were commonly used for jailbroken devices to install apps not available in the App Store. For non-jailbroken devices, users typically wouldn't need to deal with IPA files unless they're looking to install an app version not officially available.
This also rarely works now, as Netflix requires DRM modules and modern web standards (HTML5 Encrypted Media Extensions) that the iOS 5 version of Safari does not support.