So, is it safe? The answer to the question would be (as usual): It depends.
If you're just a generic Joe Blow who wants to make sure your private pictures don't get viewed by your collegues or kids, you're golden. The fact that the there's no way a software-only attack can get the pincode means that some hardware-experience is needed to start hacking the device, and that will deter casual onlookers enough to make the device completely safe for curious neighbours or collegues, even if they are smart enough to, for example, install a keylogger on your PC.
If you're a business-person with actual info to hide, info that could financially benefit other parties... you can still use this, but make sure to pick a strong pincode. More than 11 digits should do, depending on how badly others want the data.
If you're, say, the president of a nuclear country and want to use this to carry around the launch codes of your nukes, I wouldn't recommend this device. While the thing is safe for a casual hacker like me, someone with money or the resources to de-cap chips can probably get to the data fairly easy: the PIC which contains the keys to the HD is not a secure device and when decapped under a microscope in a laboratory can probably be made to give up that key fairly easily.
Aside from the bruteforcing probability, the evil-maid-attack still is a factor too. If someone has the engineering skills to create a microcontroller to catch the PIN or the HD-key and is willing to break in twice to solder it in, put back the HD, wait a while and then steal the HD, the enclosure won't really stop him from doing that. Ofcourse you can wonder how common such a scenario is in real life, but it may be a good thing to keep in mind.