Yes the M4 is a lot cheaper, but I would say it is not the right gun. it is true that the AUG has low fps, but you can just replace the spring. Also the AUG is more accurate, and is better for addons, I will not talk about the internals since you have already talked about it, but reliabilty, is what ECHO 1 lacks. With a Tokyo, you are almost garenteed always to have a good gun, but not with the ECHO 1, because you dont konw if you will have a lemon. Since I do have a ECHO 1 M4 (which I dont use any more) I know about it. It is fairly accurate, but sometimes you will spray about ten bbs, and the eleventh will just roll out of the barrell. Also the barrell wobbles, a fair amount. For me the hop up needs constant adjusting, but it is fairly easy to reach. Watch out for the foregrip on the M4 since it is made of cheap plastic, and sometimes the stock falls off. ON the AUG it is a non wobble gun, and is accurate, more expensive, but jams less. The battery compartment is better on the AUG then the M4, my vote is on the TM AUG