It's a good idea. I just about signed up and then you want a credit card so I stopped because your site is http. You are probably using stripe so it's not a big deal but that's a problem for me. Try freemium. I think you will get 10x amount of signups.
I think the platform is good. It's simple and easy to read. The content is just RSS stuff so try to add something interesting. Checkout https://www.zublim.com. They are working really hard on getting quality content that's not just murders rapes and wars. But I think your layout is better. Without good original content nobody will use it.
Another resource for mandarin specifically replacing flashcards for simplified characters.