Regarding the 2020 Gear Guide. I believe that Scuba Diving/ScubaLabs has always tested equipment sent to them by the manufacturer. For a manufacturer to participate in reviews, they would have to supply the equipment. Many of the manufacturers who supply equipment also appear to be advertisers. In many ways, that is not a surprise. I have always wondered what the influence of advertising had on the content of the reviews, I have no personal information.
Though it has always been apparent that Scuba Diving contained a lot of advertising, I never paid much attention. There is a dazzling amount of advertising in the 2020 Gear issue. The following all have 2 page ads: Seiko, Aqua Lung, SeaLife (plus an additional smaller ad), Sherwood/Akona/Genesis, and Gull Diving. The following have 1 page ads: Garmin, Oceanic, Scubapro (2 one pagers), Cressi (2 one pagers, including back cover), Mares, Tusa, Seac, Mares (2 one pagers, one for rEvo), Salt Life, Bare and Bare. Many more have partial page ads including Shearwater, Big Blue, Spyderco, Fourth Element, Ist Diving, Dive Rite, Pinnacle, Venture Heat, Truli Wetsuits, Gpacers, OTS, and Spare Air. Wow, that's a lot of advertisers!
Most of the products in the reviews come from the advertisers, but not all. There are products from Suunto, Apeks, Stahlsac, Underwater Kinetics, Atomic, Hollis, Zeagle, Head, Waterproof, and LavaCore included. For some categories a certain manufacturer seems to be significantly overrepresented. Spyderco has 6 of the 8 knives listed. Gull Diving (a company I had never personally heard of) has 8 masks listed and also has 2 fins and the only 2 snorkels. The examples of Seiko watches and SeaLife lights and cameras have already been mentioned by others.
So, everyone can make their own decision whether to subscribe and/or read Scuba Diving. I have never paid much attention to the advertisements and the reviews have not played any role in my equipment choices.
For me, there are two exceptions with regard to the value of the ScubaLab equipment reviews. I have found the hyperbaric chamber testing of dive computers and the ANSTI testing of regulators to be objective and of potential utility. Both of these topics have been relatively extensively discussed on SB over the years.