FWIW, I used to write features and a monthly column for a car magazine (not the most main-stream, mind you) and never once had any pressure from my editor or the publisher about what I ought or ought not to say. There wasn't generally much need to say something an advertiser or client would react badly too, but the writers were free to do so if they felt it was justified. Honest John has often quite scathingly criticised a range of car makers and has reached a high level in his profession as a result.
HJ is the main reason I buy the Saturday Telegraph each week! I feel very confident in his opinions. Remember when he challenged the major Supermarkets over their quality of fuels sold.? Said he'd retract his statements if they would confirm otherwise to him in writing. I'm not aware they ever did.
The only thing I think he got himself in a bit of a mix-up over once was re Varifocal lenses. He realised his predicament and printed "Topic closed". I've NEVER see that before or since on any other subject!