You may not know it, but there is an unforgivable sin being committed by a number of mobile websites. I ran into a tweet that sums it up, as follows:
When mobile websites automatically redirect me to the app store to get their app, I file them away under "Never Visit Again."
— Jonathan Everitt (@jgeveritt) March 16, 2014
To be honest, many visitors do not want your app. They just want to access some quick info on your site and be on their. Or something like that. Forcing them to the app store to download your app is one way to ensure that they will almost never return to your site. It does not matter how friggin’ awesome that app is. Instead of imposing a redirect, give visitors and users of your mobile website the option to click on a link or button that takes them to the app store. Never impose it. Ever.