I now realise that my board doesn't exactly resemble some of the other Mega 2560 boards advertised on eBay.
Could someone please help me here, by clarifying whether or not there are more than one variants of the Mega 2560
I keep getting "Your attachment has failed security checks and cannot be uploaded. Please consult the forum administrator."
No official Arduino boards are sold on eBay.
The official board only has one variant.
There's no telling the difference between the many clones on eBay.
You could always use the one of the many image sharing services like imgur and post a link.
The metal can is the crystal for the CH340G USB-to-serial adapter. Your Mega 2560 is a derivative of the genuine Arduino Mega 2560. There are also clones of the Mega 2560 on eBay. A clone is an exact copy of the genuine Arduino Mega 2560, except they are not supposed to use the Arduino logo. The clones and genuine Arduino brand boards are a little more expensive, because the ATmega16U2 chip is more expensive than CH340G. Your derivative with the CH340G needs different drivers on your computer compared to the ATmega16U2. Since you are using it and it works fine, you have already installed the drivers.You may see other derivatives which make use of alternative USB-to-serial adapters, such as FTDI chips. But the most common variant is the CH340G because it is extremely cheap. Only advanced projects make use of the ATmega16U2 by programming it using the header pins behind the USB connector. Advanced users can do things like move the mouse cursor on the connected computer or simulate a keyboard and initiate keystrokes to the connected computer. Your CH340G is not programmable. If you don't plan to get into that sort of advanced use, you probably won't notice any differences between your board and a genuine or clone board.
No official Arduino boards are sold on eBay ...