mo' better", in a kalashnikov, must be quantified.
a good quality sar 2 and an ak from orf, inrange, igf, independance arms, ak-usa etc. will function and shoot so close to the same as to be indestinguisable.
the custom builders apply the details that make the differences for your extra money.
most builders apply a much better finish. a reasonable parkerizing job at the least and sometimes an overcoat of gunkote, molykote, laquuer or other paint-like finish that is applied over the parkerizing.
some builders will refinish the wood or fit out a different furniture set.
some builders will add a muzzle device.
some builders include a plastic hard case with their rifles.
some builders install a higher quality fire control set.
some builders will correct any build deficiencies that a base rifle may have been shipped with.
some builders will offer a warranty with the purchase of their rifles.
depending on the dollars involved (a builder really can't do much on a $100-125 margin), you can run the spectrum of near bone stock/refinished to a museum piece.
since it sounds like you are after a shooter grade kalashnikov, ask orf what extras are included in their $400 rifle.
going by the pic on the website, it would appear that an ak-74 style muzzle brake has been added to an sar series rifle. i cannot tell from the picture if it has been refinished. i do not see a cleaning rod in the picture.