This odd taxi special is just 9 minutes straight of the manager and one of the idol girls talking to each other while sitting in a room. The conversation is about the word 'flauntingly' and some other topics that come up. It doesn't really add anything to the main anime at all.
There isn't much in the way of animation apart from moving heads, mouths and a face roller but it's in the same style as the anime. The voice acting is also the same as the main anime.
Overall there really is no reason to watch this conversation. It doesn't add anything to the main anime, it isn't impressively animated, it's just a 9 minute conversation between two characters; which sounds kind of neat putting it like that. It may be worth watching if you're looking for something relaxing for 10 minutes but for most people this probably isn't worth watching.