How popular is the new Twitter #music app? Well, at the time of writing (Monday morning) it’s the ninth most popular free iPhone app in the US App Store chart – ahead of even Google Maps, YouTube and Instagram. Not bad a few days after launch, but analytics firm Simply Measured has some more datapoints on how the app is actually being used, through the #NowPlaying hashtag that its tweets generate. It notes that just over 256k #NowPlaying tweets were pushed out in the first 24 hours of Twitter #musicbeing available – “four times the first 24 hours of Vine posts” according to TheNextWeb. Simply Measured has also tracked the number of tweets being generated from the app by specific services, with Spotify narrowly edging out iTunes, with Rdio some way behind. Not a big surprise, given these services’; respective audiences. However, Twitter#music’s value will be judged over a longer period.