Apple became the world’s leading vendor of wearable bands in Q2 2015, overtaking brands such as Fitbit and Xiaomi, according to Canalys estimates. With 4.2 million shipments, Canalys says that Apple easily overtook Fitbit, Xiaomi and all the smart watch vendors, despite the Apple Watch’s significantly higher pricing. The research firm says that the early release of the WatchKit SDK to app developers has helped the expansion of the Apple Watch.

However, early sales were hindered due to two factors. Firstly, Apple missed the Q4 2014 holiday season. Secondly, supply constraints stalled shipments for the first couple months after launch.

"The Apple Watch is the most sophisticated smart watch to date, and it has proved popular with Apple fans worldwide. But Apple and other vendors still face important challenges to make the smart watch a breakout hit. Improvements in performance, battery life and sensor integration are needed to make future models more attractive, but it is the quality of third-party apps that will determine whether the Apple Watch will be a long-term success," said Chris Jones, VP and Principal Analyst at Canalys.

The report came as Apple readied its quarterly earnings report for Tuesday release.