I've worked with both G&P and KA products, quality is very similar (i.e., excellent) for both. I believe the KA stuff is a bit lighter, possibly more aluminum in their construction.
One of the major differences is that the G&P barrel will have a 14mm+ threading (while most barrels and accessories have 14mm-); if you plan on using silencers or changing your FH, this may be something you may want to consider. Also as you can tell, the KA handguard has the metal heatshield.
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