I need an Arduino Mega 2560 (that is the one that has more pins). I went to eBay and there are a lot of different boards. I'm thinking of buying an ATmega2560-16AU CH340G MEGA 2560 R3 Board + Free USB Cable for Arduino . Is this one good? I mean, does it do the work? Is it compatible with the Arduino IDE? Anything I need to know?
The Chinese boards generally work just fine with the official Arduino IDE. One thing to be careful for though is the bootloader. Most the time the Chinese vendor had written a custom bootloader, which may make certain pins behave funny. e.g. a common thing is for pin 13 (the default LED) is permanently high.
I would be very cautious ordering these boards though. Most if not all of these breech the terms of the open source license which Arduino is released under. Besides that, ordering these boards you are supporting the Chinese slave labour gone into manufacturing this board for extremely low prices.
Why not purchase the official Arduino boards? Not only do you get quality boards, but you are also supporting the open source community, and ethically manufactured electronics.
The Arduino creators have spelled out their position on clones in a fairly lucid blog post a few years ago.
Your board comes pretty close to being a legitimate clone, but the claims about being manufactured in Italy are almost certainly false and possibly illegal.
I bought a CH340G based board myself, and apart from needing to install a different driver, it's pretty close to the original (There are a few projects that reprogram the 16U2 on a real Arduino board, but the vast majority of projects use the 16U2 as a straight serial converter, and the CH340G seems to do that job OK).
As other answers have pointed out, clone makers don't contribute to the community, so consider buying a real board occasionally. On the other hand, Arduino Mega clones are literally 25% the price of the original, so for that board, going with a clone is certainly tempting.
There is no way to know the quality of the Arduino clones on eBay. They may be fine but you never know.
I recommend buying an official Arduino from one of the official distributors.
There are good quality Arduino compatible boards like the SparkFun Redboard or the Adafruit Trinket. But these are not made to look like official Arduino boards. (Neither of these would work for you since they don't have as many pins as the Mega)
You could buy an official board, but if you're worried about the price, I wouldn't go for the EBay ones. There are other better clones out there. For example, I know that SparkFun makes their own Arduino Uno board, and while it's not called the Uno, it works exactly like it's supposed to, without any surprises. From what I remember, it's cheaper than the official Uno too.
I bought some of those boards and have had no problems with them. They are not as some claim, counterfeit boards. If they were, that would mean that the 'arduino' boards are not open source. I have also never seen any boards claiming to be built from italy. They are specifically labeled "Made In China".