Doing some research on this in the context of dev newsletters/dev products.
If you did buy or started using the product after seeing a newsletter ad, I am wondering if you remember what you liked about that ad. Or if not liked what made you not skip it immediately?
If you are on the founder/marketing side and you ran ads in dev-focused newsletters which ones were more successful?
Newsletters aren't an exception. The only conceivable exception is when it's like 'Hey, I really enjoyed this newsletter' or affiliated interesting looking newsletters(eg I've looked at the other newsletters Nature has, which are linked to at the bottom of Nature Briefings), but those aren't really ads.