I have been a subscriber to GT since '98. I find the magazine to be VERY helpful and informative. It seems to be fair and doesn’t pull punches if something they test is junk.
The format will usually have a handgun, rifle and shotgun comparison. With sub-topics for each such as compact .45's or AR-15's or over-unders. There is usually a gear write-up and maybe an ammo one too.
They then takes several different manufacturer and models and puts them through tests using different ammo and such and then reports on the findings.
Not sure it's "scientific" testing but it gives you a pretty good idea of how the different models match up.
Overall I think it is head and shoulders above all the other magazines as far as ratings of firearms, gear, etc.