The name isn't exactly ideal... Searching Google for "SmartKanji" turns up smartkanji.net as the first result, a website which is clearly unrelated to yours.
Either way. Looking around the site, my first impressions weren't very good to say the least.
- The introductory text is written in all caps (= yelling) and disappeared by itself before I finished reading it.
- The site offers 9 levels with 9 kanji each, meaning 81 kanji total, not 500 as claimed. Apart from 一, not even the number kanji are included in this.
- This vanishingly small amount of kanji actually reduces learning efficiency. 思 is easier to remember if you already know 田 and 心, but 田 is not included. 心 is, but only comes much later.
- There's no search function, either for kanji ("what were the readings of 前 again?") or for sample words ("how do you pronounce 一般 again?").
- There are no hints for remembering kanji. No component breakdown, no mnemonics, nothing.
- Going from one kanji to the next is highly cumbersome. You need to click the "Back to circle" button (as using the browser's Back button gives a form resubmission error), hover over the Learn button to reveal the kanji (why aren't they visible from the start?), and click the next one. It gets worse when you reach the end of a level. Simple "Next" and "Previous" links at the kanji level would be much more user friendly.
- The language dropdown contains three-letter language codes instead of names, doesn't contain "English", lists the currently selected language twice, and also lists languages for which a translation of the current kanji is not actually available. The first time I changed the language I also got a PHP error (though I can't seem to reproduce that one anymore).
- There's no way to go back to the top page from a "Play" page. Manually removing everything after the domain name in the URL results in a redirect to the SmartKanji blog, which has no link back to the learning page.
- Each example word is accompanied by two sets of "Buy now" buttons (which are in Danish regardless of the selected language). Are you telling me you expect money for the translation of these sample words (something any online dictionary will do for free) and bookmarking them (a builtin browser function)? Really?
There's a lot of work to be done before this site will become useful. Right now, it's sadly the worst kanji learning resource I have ever seen. Even if you struggle through the UI and its 486 sets of payment buttons, in the end you get less out of it than the first book of the "Genki - an introduction to elementary Japanese" series; that is, nowhere near enough to "read 70% of most Japanese content." Sorry to be this blunt, but that's how it is.