It is usable and the speed is quite good. There are fewer customization options for the title, and it is not possible to mark whether the resolution is the source resolution or 540p. seems it always download the source resolution video

使い易くて良い！　ただしプライベート動画は 投稿日時が取得できない様で ”00” になってしまうのが残念です。 ※ver 1.3.1
It's easy to use and great! However, it's a shame that the posting date and time for private videos can't be retrieved and ends up showing as "00". ※ver 1.3.1