I had some problems getting it to work primarily because the English instructions I got from the website was very poor and I could hardly understand it. I did some trial and error until it eventually worked. It has an Auto, On and Off option, and under Auto it is supposed turn off when your computer is off. However, at least for the Mac, it remains open even if you put the mac to sleep. This can be problem because, as I stated in the title, it is quite noisy, so I can hear it at night (I don't know what it does at night when my computer is not accessing it.
Price was quite good in amazon compared to the electronic shops in Japan. Probably not as hassle free as getting a time machine but its advantage over the time machine is you can access your files away from your home (which you can only do in time machine if you subscribe to mobile me).
Other than the cons I mentioned, it does its job. Speed was not noteworthy, but maybe only because I was migrating tons of gigs from my hard drive to it.