I am a pround owner of an ares tar21.
I suppose the bad ones are the CTARs (short barrel with mars sights), I own a standard length one and got it off 2nd and i am so pleased with the gun overall.
it has solid construction and shoots great, eventually my hop bucking must be wearing down abit but i believe with a new bucking this gun will out range most g&p m4s and i did a A B test alongside my friends brand new Troy M7 and we both shoot the same where mind is a second hand.
the only problem u need to bear in mind parts are difficult to find and some parts are proprietary such as the gearbox shell, cylinder( correct me if im wrong).
from my understanding the Ares one has been out of stock for quite awhile thats why i got a 2nd hand, u might try getting a Elite Force Ebb one, held one before in HK and it looks, feels totally different from the s&t/explorer version.
It is as solid as the ares one and much balanced weight since the battery is front placed.