I have been running my VFC m4 five years now, hop up & gears went around same time three years in. Replaced both parts working fine every since. Note with VFC's I found that the mid cap magazines made by VFC work the best for feeding. Every clone brand or cheap magazine i'v personally used either doesn't fit right or feed well. Personally experience on that though, cannot say the same for everyone. Externally no problem & would recommend VFC to anyone in that price range.
Look into krytac, like stated above they are coming out with some great features out of box from what i'v read. I have not held one or fired one yet though. If I was buying a new M4 in that range I would look seriously into krytac if I was not going to upgrade it until something broke.