Twitter’s music discovery app hasn’t been faring too well in the App Store charts recently, but how popular is it in terms of usage? Mobile data company Onavo has published some stats through its Onavo Insights tool, estimating that Twitter #music was being actively used by 1.18% of US iPhone owners in April. Is that good or bad? Well, we can cross-reference that stat with separate figures from comScore claiming there were 49.6m active iPhone users in the US in March. If that stayed relatively steady in April, Onavo’s data indicates around 585k active Twitter #music users that month. The problem: the app was only released in mid-April, so ‘active’ means ‘anyone who downloaded it to try it out’. The real test will be how many are still using it in May and beyond. Onavo Insights offers US iPhone penetration stats for other music apps too: 32.3% for Pandora, 19.2% for Shazam, 8% for Spotify and so on.