The app itself is really easy to use. However, updates are needed. A new line opened in October - its December and theres still no update. As a PAID app, this should have happened immediately. Some of the travel times are off - it takes way longer than 16 mins to get from Seoul Stn to Incheon Airport even on the express line. Additionally, it would be nice to have a feature to view travel times with alternate routes, or to create a 3-legged trip..
Waegook about Seoul City Metro - Seoul, South Korean Subway Guide, v1.2