The Apple HDMI adapter costs more for a couple reasons. I'm glad I spent the money.
1. Supports iTunes and copyrighted video! (other adapters usually are not mFI certified. If the description has you accept a compatibility warning, it's not Apple certified. they do not pay royalties, which means they won't support copyrighted or DRM movies such as iTunes, Netflix, Amazon video, HBO, etc. )
2. it powers itself off the iPhone or iPad. Very power efficient too. (other adapters require a USB power adapter and they run hot)
3. This adapter is really an external video card. It has a GPU and 2gb ram ( the specs are better than others. This means when working correctly the phone should not slow down, freeze or lag anywhere near as much as other adapters cause)
4. The adapter automatically receives software updates from the phone/iPad without you having to do anything.
5. iOS allows separate audio output, so the video can go down HDMI, Audio can be HDMI, bluetooth or Airplay speakers.
6. all TV resolution format config is automatically the best available.
7. apps that support external monitors run simultaneously with the phone and full screen on the TV. (Presentations and games aren't simply screen mirrored and cropped with the black bars like some adapters ) Obviously Apple apps work great, but YMMV on whatever 3rd party apps you use.
I'm very happy with the Apple adapter, but deduct 1 star for the following reasons.
1. Zero included instructions. There is a very specific connecting order one must do for it to work. First set the TV to HDMI input, then cable the HDMI to the adapter, then cable the adapter to the phone. anything else, blank screen.
2. The software update is so hidden that you have to look in settings -> General -> about this phone -> scroll all the way to the bottom to see the adapter menu and open it. Also this software update could take a minute or so the first time you plug it in. and you'll have to disconnect and reconnect a couple times for the newer software to take effect.
3. The HDMI resolution is unavailable to the user. If the TV does not properly tell the HDMI adapter what resolution or formats it can handle, then the apple adapter defaults to the lowest quality possible. This is common when plugging into a home theater setup and not the TV directly. If your resolution or quality is poor, unplug start over plugging directly to the TV to the adapter, then to the phone.
4. Apple does not include a couple feet of HDMI cable built in, like the old analog iPod AV adapter did