So, the question is: will covering up your on-board camera actually help? Well, yes it will in the sense that the camera won’t be able to ‘see’ anything, but no it won't in that it will still be able to hear what you or others are saying. And a more fundamental problem is that if you have been hacked, there are also bigger problems in terms of what could go wrong that just worrying about your webcam.
Remember, the webcam itself will see you and your face, and (in modern integrated devices) hear conversations. Unless you are doing something embarrassing, or having a conversation with very confidential content, although bad, it’s not the worst exploit or hack that could happen.
Hacking your device can occur through exploits that leverage weaknesses in the operating system or application software running on your device (which is why regular updates are so vital), through clicking on malicious links in emails (still a surprisingly popular attack for hackers), via poor ‘perimeter’ security (your router is configured incorrectly or has a bug in it), through giving someone physical access to your device (they use a dodgy usb stick, or browse to unsafe sites), and so on.
If you don’t do any of those things, and got your computer or device originally from a trusted source, we would argue that webcam / camera hacking is still a low risk event. But, it is still worth covering up providing you don't forget about the other risks and problems that can occur!
Where it might be more useful is when you use shared computers (a friend’s, one in a hotel or conference centre, and so on) – here, covering up the webcam could well be worth doing. Or, if you yourself are - for some reason - a likely target. Clearly, Zuckerberg is. Me, no. But perhaps you?
The above has been written from the perspective of computer usage risks. But, as a promotional product, this is still a very neat idea. For example, the mobile phone is always used during the day - the benefits of having a branded item on the phone are obvious. For those companies and organisations that want to reinforce a security message, this could be a powerful way of spreading the word.