I've been reading CU's auto reports for about 30 years. I was even a member for several years. They are honest, but some of their technics are questionable. The good thing is that they fully explain how they test--They test--you decide.
A few observations;
In their annual survey, they used to ask subscribers if they had any trouble with their new cars which THEY considered major. Some of us consider problems like sticky window regulators or even a transmission that shifts at the wrong time as normal things that need attention. Other people consider a faulty dome light as a MAJOR problem. Perhaps the statisics average this out, but perhaps, not.
Some interesting statisitcal things appear, and lead to some people thinking that CU has a bias. I remember one year that the Ford Explorer was rated as "poor" but the absolutely identical Mazda Tribute ( same factory, same assembly lines, same personel) got a very good rating. That may be more reflective of the dealerships than the cars, but identical vehicles should not get such differing ratings.
In their 35mm SLR camera ratings ( many years ago)they measured how much the camera back flexed under a certain weight. I always thought the way to rate cameras was to take pictures with them.... ( If I was going to drive nails, I'd get a hammer, or at least a Nikon F1)
As always, take their comments with a grain of salt, and ALWAYS read HOW they test. That gives you the information you need to evaluate their results. Its all there.