Great app for an e-commerce site like ours, However, few key customization features are lacking (Ex: ability to modify the type, color of the submit button and the email text box.
Works great but remove the Console API from the main context which is stupid.
If all you're going to do is popup an image that is designed to promote something (e.g. "5% off today only", or "Use code XYZ to get a special offer", etc.) then this app is a great value.
If, however, you want to gather emails and integrate with MailChimp them you should know that you have to opt-in to their highest paid plan.