This is Drew with Memberful. Good question. Here's how we're different:
* Integrate with your Stripe account. You get to sell with a processor you love (Stripe) and we act as a nice layer on top of that. This means you don't ever have to worry about us touching card data or storing that type of information.
* We're not venture funded. We built a real business on this software (see http://thethemefoundry.com). We depend on it everyday. We plan to build this service the right way (even if it takes a little bit longer) and stick around for the long haul.
* Completely customizable. Memberful uses Liquid templates and a theme editor to give you total control over the checkout and account screens. You can tightly integrate the design with your own site (again see http://thethemefoundry.com) and customers will have a completely seamless experience.
* Recurring billing / subscriptions. Sell monthly or yearly subscriptions quickly and easily. Customers can view their account, update their card, cancel / renew their subscription, etc.
* Simple WordPress integration. We built a WordPress plugin to sit nicely on top of our API and provide point and click integration with WordPress. Customers are automatically signed in to your WordPress site and your products and subscriptions are synced up with WordPress and ready to use. Protect specific content or entire posts and pages.
* Use your own email service. We'll send emails for you by default, but you can use your own SMTP server or service (Postbox, Mandrill, etc.). Emails come directly from you, giving your customers an even more consistent brand experience.
Hopefully this helps. Happy to answer any other questions!