Since there is a pile of information out there already I am just going to clear up a couple things that bothered me before I bought it, things I had a hard time finding out online. So really quick and dirty and without pics since lots can be found through google.
First a note, ECHO1 is a rebrand of KART EBR's, AGM is NOT the same. AGM have a non-standard hopup design and even cheaper internals.
Okay, so to start its all cast potmetal, no CNC, no 6065 aluminum like G&P or KA. On that note its still really solid, zero wobble anywhere, and weighs as much as a brick. In my book pretty good since it retails for US$125-250.
There is one exception to the no wobble rule, the front handguard. The one that holds the battery in and is screwed onto the lower frame. It wobbles quite a bit and I really don't trust a 9x2mm piece of low grade steel to hold the battery on and I will be gluing the handguard into place and rerouting the wires to a PEQ.
I heard all these comments about it not having a TM hopup, using some messed up inner barrel, and having a slightly non standard mechbox. Well it is a direct TM clone down to all but one detail (explained later.) You could drop a TM M14 assembly into the frame and it will be a perfect fit, I know it will because I dropped in my TM M14 sniper setup into the EBR chassis and it fit fine. Only thing to worry about is the wiring since the EBR is wired forward and a normal M14 is wired to the rear. All external wiring so easy to fix even without a soldering iron.
The mini connectors they use have less metal in them than normal mini connectors I have seen, made one smoke a bit when I plugged in a large 9.6V battery. Replaced with deans.
Hopup is indeed a TM clone, no worrying about getting a TM hopup and inner barrel (though a G&P M14 hopup is a lot easier to get.) It seems to have a standard brass inner barrel, I guess 6.08mm, SOCOM length (440mm?) The hopup rubber is garbage, replace it with a good one when you can.
Motor is crap and can barely turn over an Ms110 spring, label on it is the same as a CYMA I had, the English on it reads: "Chaoli Mirco-motor machinery co ltd." Motor is soldered on.
There are two tiny little bolts that hold the back end on the gun, the part with the grip and the far rear rail bit. None of this needs to be taken apart to get the mechbox out of the gun so I will be epoxying it all together to make it more rigid (except the slither stock obviously.)
Flash hider is +14mm, so get an adapter or make sure whatever you want to put on it is +14mm, same threading as PTW's and G&P outer barrels.
Charging handle sounds a little higher pitched than my TM, probably due to cheaper metal, though it still put ANY other AEG to shame for charging handle noise.
Inside the mechbox it is all TM standard except for one detail. They managed to redesign the shell to accept standard ver.2/3/6 gears instead of the ver.7 specific gears needed for a TM gun. It has a full sized spur gear inside instead of TM's undersized spur gear. This means more torque. On the note of gears, the gears are in fact not xti/xyt that many guns have (STAR included) but are the same as was in my AKS-74U CYMA, they are branded www.Gear.net.cn
and I had the axle crumble off of the spur gear on the set in my CYMA AK so I really recommend new gears. The shimming was HORRIBLE and I could move the bevel gear almost a mm from outside the mechbox. Bushings are solid brass. I dropped in Modify dual oil channel steel bushings and SystemA highspeed gears and I have one of the thickest shims on each gear plus 1-3 thin ones. Mechbox tolerances are horrible.
The piston is a white nylon one, really soft, can almost scratch it with my finger nail. Piston head is same material, ported. Cylinder is a non-taper solid brass, same length as a standard ver.2/3/6 piston where as the TM M14 piston is a mm or two shorter than standard. Cylinder head is a standard TM type, nylon with brass tube. Nozzle is crap, airseal is crap, dropped in a Prometheus and its great. Replaced piston with Guarder polycarb, piston head with Sorbo MASK, installed Sorbo pad onto a solid stainless Modify double o-ring seal cylinder head, cylinder is a Modify non-ported standard stainless chrome plated.
Spring guide is brass non-bearing, spring is a silver coloured linear spring. Spring is not fixed into the nozzle, comes out freely.
Tappet plate is clear plastic, don't know what type but I can put dents in it with my fingernail, replaced with Guarder enhanced.
I will be using the stock hopup unit, seems fine to me going over it with a magnifying glass. Waiting for a 6.03mm tightbore to come in this week so I wont be reassembling it to test just yet.
Before I took it apart, it fed fine with the stock 280rnd hicaps, my TM 440rnd hicap, TM lowcaps, Deep Fire lowcaps, and King Arms 70rnd lowcaps (110rnd mags suck so I don't own any.)
Any questions or comments, post em here and I will try to answer em. If you PM me with a question or comment and I think its relevant I will post it here with my answer without your username, just in case your shy or something.