What are the differences between those official Arduino boards & (something)dino

Hello, various manufacturers are selling things with a bit of a change in the name. For example, Kingduino Mega 2560, SainSmart Mega 2560, (something)dino, etc. What are the differences between these boards and the official ones from Arduino?

Some stores also sell the board at a much lower price, say half the price and sometimes below US$15. The photo of these boards looks the same as the original one but in one store, there is a note saying that it is not original. Are these all fake products that might not work or they are clones that do work?

Also, given that they are the same, why Arduino sells "Arduino" in the US only and "Genuino" outside the US? I have never seen Genuino.

Generally the components needed to make an arduino are relatively inexpensive and as such are cheaper to buy from china, however often you can run into bugs with the bootloader, though i personally bought a real arduino, for my prototyping, i use cheap clones in my actual projects. some of the other board types also have additional functionality built in, wifi gps etc where you would normally need a shield for this.

the official versions pay royalty to the makers. this keeps this list going as well as research and more.

the clones are just copies.

most of us own at least one official version so as to respect the work.

as for the genuino. the name Arduino was stolen and copyrighted internationally.
long story, but genuino is the only one that pays royalties to the makers.

the boards are open source, that means anyone can use the exact layout and the exact parts list and make an exact copy. even you, if you need to make a copy for a project and want to add features on your custom board like wi-fi or some such.