Despite this mouse now being a couple of years old and weighing 145g (and if that's not enough it does come with extra weights) it is still one of the most popular ones out there and this is for a very good reason: I've had this mouse now for over a year and have had no issues.
The G502 has a very angular look which makes this a very good looking mouse, if that's an issue for you. It is definitely best for a palm grip as the thumb wrest just below the extra buttons and the rubber on the right side of the mouse make it very easy and comfortable to grip. You could use it with a claw grip but then the weight does become a bit of an issue. The matte plastic finish also holds up surprisingly well to stains
This mouse also has a lot of extra buttons - two of these are just above the thumb wrest and there is a "sniper" button at the end of the wrest (it lowers the dpi to make it easier to hit those headshots). There are two more to the left of the left mouse button, one behind the scroll wheel and the scroll well has the standard middle click as well as left to right for even more buttons just in case the other 8 weren't enough.
However, by far the best button on this mouse is the scroll wheel lock. It allows the scroll wheel to switch from notched scrolling to roll freely which is glorious for scrolling through spreadsheets, long news articles, daily mail etc. I just wish more mouse manufacturers included this understated feature. On the the whole the buttons feel good and are easy to press although the ones by the thumb wrest, especially the "sniper" button can be a little hard to get to when using a palm grip. That said the position of the buttons, especially the side ones, is much much better on the Deathadder.
One of the main selling points of the G502 is Logitech's own sensor, its so good that you can get 12,000 DPI with any smoothing, acceleration or jitter. Even though 12,000 DPI is ludicrous it does show the capabilities of the sensor that it can hit that level and still perform perfectly. You can also use their software (which doesn't quite beat synapse) to carry out surface tuning, this in theory allows you to get the lift off distance to lower than 1.5mm. Their software also has the features you'd expect such as keybinds, macros, profiles and sensitivity levels.
As I already said this moues is heavy, really heavy. At 145g it is 40g heavier than the Razer Deathadder which for some people might be better personally I have found it to be a little bit too heavy. It also comes with several extra weights, these in theory allow you to customize the feel of your mouse but in reality their a bit of a gimmick and i couldn't really notice much difference that would actually affect gameplay.
Yes, like everything coming out today there is an rgb version called the G502 Proteus Spectrum, there is no difference between it and the normal non-RGB mouse apart from the fancy colours (16.8 million to be exact) and if you want an RGB mouse I would say there are better options out there, there simply isn't enough lighting on this mouse to make it worth it in my opinion. You can see an example of the RGB below:
Due to its weight and slightly inferior design I would say that the Deathadder is a better mouse. That said if you want a heavy mouse then this is definitely the best one out there and if you're looking for a mouse that will last a long time then this is also a very good choice.
You can buy one now on amazon here.