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.
That said it could still land a message/spark interest.
And perhaps if it is worth investing your time in, you'll hear about it again, hopefully from a source you trust.
It could. Smithsonian's newsletter often has ads from 1440 in it, and I've been considering looking into them more, but mostly because they say they're free. If it was paid, I'd probably stop looking into it, or look to see if the local library subscribes to it or has it (as I often do with books). So, from the advertiser's perspective, I'm not very helpful - the best you'd get is increased library circulation.