Main downside is this they already have you as a customer. A lot of these efforts are buffoonish and try to sell you shoes/eyeglasses/appliances after you just bought what you wanted from them.

High value honest and transparent ads can work, like say "Will it blend" or providing field related instructions good enough to essentially be the canon to say synthesier configuration and maintenance.

That is hard and bespoke. Meanwhile crap ads are very easy and adaptable. So long as there is a positive return being a menace or nuisance to the commons can pay. As spam infamously shows.