I'm using WordPress 3.6. and just tried to upgrade to Version 6.3.1 of your plugin, but got this fatal error:
Cannot redeclare format_price() (previously declared in /home/mysite/public_html/wp-content/themes/wp_penelope/panel/generic.php:566) in /home/mysite/public_html/wp-content/plugins/app-store-assistant/includes/app-store-functions.php on line 462
It appears there's a conflict with the ecommerce theme I'm using (cssigniter.com/ignite/themes/penelope/), due to both your plugin and the theme using "format_price()".
Is it possible that you can perhaps uniquely rename your price function in your plugin, so as not to cause this kind of conflict? I'm sure others will run into a similar issue. Maybe, "appStore_format_price()" (similar to your other calls), instead of just "format_price()"?
As a workaround, I renamed the function call in my theme, since I'm not using its ecommerce features on my site, and it seems to have worked. I was able to upgrade and activate your plugin this way.
Thanks for a great plugin!