I have a 556 and with the Swiss style furniture it's not muzzle heavy at all, less so than most M4 clones with heavy barrels and railed forends, that's for sure. Not to mention it has a true folding stock, and cost only $850, less than most M4s as well. Eats everything, including crappy wolf, about 1000 rounds through so far with no cleaning or lube. Just took it out of the box and started shooting. Most of the complaints about it are from folks who've never held or shot one, just passing along what they read on the net.
You'll read the same about the MSAR STG-556. Yet I've got the same # of rounds through, again out of the box with no cleaning or lube, and it's been fantastic. Probably my favorite 5.56 rifle actually. That's why I take the "internet consensus" on guns with a grain of salt, as they are often wrong.