I hate pop-ups with the fire of 10,000 suns. I have never signed up for anything via a pop-up. I nearly always back-button out of the site and never come back. For news sites, I might look for an X and click it off to read the page. If I want a book, I'll find some way to get it, and I don't need a signup list or a pop-up to remind me about it.
If you want to know if pop-ups work, try split-testing. Run pop-ups for about 2 months, then try 2 months with just a signup link pinned to the top of your Home page or landing page. See which gets you more signups.
Frankly, I'm very skeptical about the usefulness of mailing lists. It's very hard to separate out profit made from a mailing list vs. organic readers who buy your stuff when it's new because they follow you on Goodreads or heard about your new release from their book friends, or because they've signed up for a new release email directly on Amazon, or if they're new readers who just found it on the 30-day new release list on Amazon, or if they've picked up a permafree from you.
Some authors have tried to separate mailing list profit out and have reported their results on KB in the past. The number of opens tends to be a small portion of their total list of signups, and click-throughs a small percent of the opens. Of course not everyone who clicks through is going to want to buy. By which time you're often getting down to a very small number.
I have carefully looked at the results these authors have reported, and I've calculated the monthly costs for mailing list maintenance plus time and labor spent for maintaining that list, and subtracted the profits from the books sales they report for their new releases, and the profits I've seen equal a few days working at McDonald's for minimum wage, when all the costs are taken away.
I think there's a lot of wishful thinking involved in the whole mailing list approach. Mailing list costs eat away at your profit every month. It's a set fee you're stuck with once your list gets above a certain size. I suspect a lot of authors go mentally vague and fuzzy when faced with these costs and don't want to think about them. Add in costs involved in editing and cover design, and yeah, I think there are lot of authors who are underwater as far as profit goes. Yes, there are authors who make money who do have mailing lists, but I really doubt it's their list that's generating the large majority of the profit.
There's one big important thing about mailing list costs. Editing fees and cover designs fees are a one-time only payment. Mailing list costs will dun you forever. They really, really add up over time and zap you hard. If you think it's just a small thing every month, in the long run it won't be that way. It will cost you far more to keep your list than it ever will to pay the for the cover and editing, even if you thought you paid a lot for the latter two in the first place.
I'd advise calculating 10 years' worth of mailing list costs, and staring at that number long and hard. Then calculate your monthly average of earnings right now, and figure out what that would be summed up for the next 10 years, and subtract it from your 10-year mailing list total cost. If you don't like the number, don't do a mailing list.