This appears, via translation to be a somewhat skeptical review of Hana. The gist we are getting is that the commentators and the reviewer seem to wonder why this is a replacement for their current solutions of using Gmail Notifier and other tools.
This is actually a fine point. Why replace what works for you? If it works, why indeed? But if there are any shortcomings in your system for using multiple web-apps, then perhaps Hana could be a solution for you. Hana is not JUST for Gmail. It is for using with multiple web-apps. One place, separate from your casual or recreational space that is your browser. Hana does not YET support notifications from your web-apps or Applescript-ability nor does it have any nifty badges about unread or new messages. Your browser barely supports this now anyway. Though plug-ins mitigate this to varying degrees.
We plan to add Growl, Applescript, Quicksilver and Plug-in support to Hana eventually. So if it isn't for you now, keep an eye on it. It might be late this year or early next year.