club.nintendo.comは安全ですか？

This domain is owned by Nintendo. It's the official Club Nintendo website (which is probably going to shutdown soon), where you can register your games or take surveys and earn coins. You can use the coins to get absolutely free downloadable games, and sometimes even DLC, that you'd normally have to pay for. You can even get free physical merch, such as posters and cases for Nintendo's portable game consoles! The available items changes every now and then, so check the date the current offers change and check back later. It's completely safe, and if you like Nintendo and their consoles, I recommend you give this a try.