Both Adafruit and Sparkfun manufacturing quality is higher than generic manufacturing from China. I suspect that most of the Chinese alternatives meet their price point by using parts that are out of spec and were purchased at a discount by the chip manufacturer (or just scrounged for free from the reject pile).

My primary example is this clock generator breakout: https://www.adafruit.com/product/2045

The board is open source and there are tons of options made in China, often on a purple PCB. I've had terrible experiences with them, over 50% of the purple boardss I've purchased fail to achieve PLL lock because of multiple reasons- sometimes replacing the crystal can get it locked, but sometimes the chip is just out of spec and can't get a lock. Occasionally I'll get a lock on one PLL and the board is partly useable. I've given up dealing with the hassle and now I just spend the extra few dollars to get a breakout that uses parts sourced from authorized distributors that meet quality control standards. Plus this gives the profits to the people who designed the board and released it as open hardware.