The overall length of it bought it then realised I'm not a fan of the long barrel but other than that it seems a decent weapon to me good range and ROF
If it's anything like the G&G SCAR-L CQC (and I believe it is) if you buy the standard one you get a long barrel, if you get the light version you get a short barrel with an extender. Either way the inner barrel should be the same length I beleive. The Light version (short barrel) is significantly shorter but the standard is no longer than a standard M4A1, the only difference might be that the RIS extends further (on the T4-18 that is).