I can't vouch for KWA / KSC guns...
But I've shot 5 different KJW Sigs and I didn't like a single one of them (all ranging from Stock, to TM fixed, to full after market overhauls). Something about them just isn't... good, in my books.
Try before you buy if you can.
Ár skal rísa, sá er annars vill
fé eða fjör hafa. Sjaldan liggjandi úlfur
lær um getur né sofandi maður sigur.