One general observation I'd make is that it's pretty rare to find a magazine which openly slags off a product or a service.
I've written quite a lot of stuff over the last few years and some of it has ended up in printed mags (none of the main UK flying mags BTW) but it always gets edited to take out anything which might upset anybody in any way whatsoever.
I suspect that a magazine, like any other business, can afford to adopt a position of utter integrity only if it has sufficient income from elsewhere. So, in my (electronics manufacturing) business I am happy to (very politely) tell any difficult customer to stick his business somewhere warm and dark, but that's only because I have ~ 100 others. Mind you, I still wouldn't do it to the 1 or 2 who make up 20% of my sales
The other thing is that a magazine "reads better" if it is aspirational, upbeat and generally avoids negative comments. That is a great policy if you are producing a mag which is scanned by its buyer in 10 minutes and then either gets tossed in the bin or spends the next couple of years on a flying club cofee table, and this what happens to most mags these days.
Yet the real world isn't 100% upbeat - especially in aviation where "participant satisfaction" depends as much on doing things right, as it depends on avoiding the serious crap. Especially in ownership. The downside of the "upbeat only" approach is that it doesn't really educate readers on the whole required picture. It is only on websites that one can do "warts and all" writeups, and most pilots I personally know tend to agree that most of the practical stuff they learnt about flying came from the internet, not from printed pubs.
In the last few years there has been a sea change in buying habits and most purchasers hit Google when they are looking for something (even if they originally saw it in a mag) and this deprives advertisers of any data on which advertising medium is actually working for them. This is IMHO the main reason why we still have so many special-interest printed publications carrying adverts; if the advertisers were to ever find out what is working they would pull the plug on most printed ads tomorrow.
So I think the mags do have to be on the whole careful what they write, but the successful ones can afford to adopt positions of integrity on the odd topic here and there. One example of that is the U.S. "Flying" mag which was critical of the Eclipse project and reportedly was excluded from their pretty significant ad budget in revenge. I recall similar cases from my 1970s/1980s motorbike days; the "Bike" mag lost all of Honda's adverts for some years, in revenge for a scathing (if 100% accurate IMHO) writeup on some machine of theirs.