No-name GBB M4 with keymod handguard

No-name (has no markings apart from serial no) GBB M4 with keymod handguard Does cycle (with different buffer spring) but unsure on reliability as I was using incompatible mags. Was bought as a project knowing it's questionable functionality but never got round to fixing it up. Don't buy this expecting it to work without fault straight away. Has a couple missing bits like safety detent.