NOTE: As of 3/15/2010, our cables have been modified to work with these GM MAF “copies”. But we still don't like them given their different behavior and lack of proper honeycombs.
The sensor on the left was pulled from an actual GM car. The sensor on the right appears to be a manufactured copy of some sort.
The two are similar in many ways, but different in many others. Some are trivial, some are not.
The first thing you'll notice is that the GM sensor has a real honeycomb screen intended to straighten the airflow through the metering elements. The aftermarket sensor simply has a chicken wire type screen that seems to only provide some crude protection from debris but does nothing to actually straighten the airflow.
The second thing you'll notice is that the one on the left works with our GM MAF cable, but the one on the right does not (see NOTE above).
This gets a little more complicated, but the core problem has to do with some electrical characteristics that are different between these two sensors. Refer to the images below (again, click image to enlarge).
As you can see, the two signals are similar, but different enough to cause compatibility problems. We do not know how well these aftermarket sensors work with a real GM ECU. We suspect that they probably work fine, but they definitely do not work with our cables.