Let me start off by saying I am brand new to this game. I have played a couple times with friends' guns, but never owned one myself. I am truly a beginner.
That being said, this is no beginner gun. The Echo 1 ST6 M4 has very nice externals, a full metal rail system, and pretty good firepower. The gun is meant to mimic an M4 used by a Navy SEAL, with logos on the upper receiver that include a frog skeleton, a skull with accompanying tally marks that are supposed to represent either kills or successful missions, and a saying: "You can run but you can't hide". This is all very SEAL-like and manly, but what I think makes it the most authentic are the inscriptions of "Duty" and "Honor" on the dust cover. The metal rails add weight to the gun, but it is not too terribly heavy. The rails seem very sturdy and do not wobble at all.
The advertised FPS of the gun is close to 400, and sure enough, mine shoots at 387 (according to AirsoftGI's chrono). This is a little confusing for me, because the gun is relatively short, making it ideal for CQB, but the FPS is too high for many indoor fields. It is very accurate, and it shoots very hard.
The box and everything inside are pretty awesome to open. The box is designed to look like an actual gun case used by a SEAL: it has fake stickers from places ST6 have been, including Kandahar, Somalia, and Bagram. When you open the box, there is padding on top of the gun, as well as all around it, holding it in place. The gun is not alone in its box; it comes with a 300-round hi-cap metal magazine with the typical wheel-winding mechanism, a winding tool for the mag and another tool that helps you adjust the front sight, a pack of 4 plastic rail covers, a plastic vertical grip, a 9.6V 1600MAh NiCad crane-stock battery, and a basic wall charger. The gun itself also comes with an attached metal rear sight that is removable as well as fully adjustable. Some of the included accessories are quality products, but some are not. The magazine is nice, as are the rail covers and vertical grip. However, the charger is very slow and somewhat unreliable, which is to be expected of a standard wall charger. The battery, though usable, was a little disappointing, as it is a NiCad battery. But it did come with the gun, so it is nice to use for now. The main disappointment in the package was the fact that it didn't have a manual. I'm not sure if it wasn't provided by Echo 1 or if AirsoftGI forgot to put it back in, but it would be nice to know the contents of it, especially for a beginner.
Sweet box design: SEAL gun box
Many extras in package: metal hi-cap magazine, rail covers, vertical grip, 9.6V 1600 MAh NiCad battery and charger
Good weight (heavy, but balanced)
Plastic is high quality ABS or polymer
High FPS: 400
Short CQB body
Adjustable crane stock
No gun manual
FPS too high for some indoor fields
Sometimes stops firing in semi-auto. When this happens, you have to switch it to auto, fire a few rounds, and switch it back to semi to get it to fire in that mode again
Biggest con is getting the butt plate off to put the battery in. Tabs holding it on to the stock are plastic, but are extremely stiff and require an insane amount of force to squeeze together enough to remove the butt plate. Not sure if it takes breaking in, but it is hard as crap to do right out of the box