Pop-ups are generally pretty obtrusive to the user experience and may actually have a negative impact on your conversion rates. I'd recommend refining and testing your calls-to-action (including offer, copy, image, & placement) to make sure those are as optimized as possible.

I'd also recommend setting up your calls-to-action as "smart content" -- in other words, show different CTAs to your subscribers, leads, and customers so you're asking each visitor to take the next step that's most appropriate for them. Happy to discuss leveraging smart content in more detail if you're interested -- it's helped us tremendously in increasing our blog conversion rates.

I also say, "No!" In all honesty, your content should convert. Focus on what you are telling the potential customer.

I would suggest that a pop-up is really not going to increase your conversions. Pop-ups are methods of last resort for poorly performing landing pages. I would instead encourage you to continue refining your messaging and CTA via A/B testing tools like Unbounce.com. Happy to talk through best practices. I have built a couple of highly performant landing pages for SaaS products.

Think of it from your prospects point of view too. If I have to sign up just to read a blog post, I will not. So, putting a pop up here is not a good idea. Also, I might already be a customer just coming to learn more about your product. Do you really want leads that are not well qualified? Because that is what you will get as there will be visitors who might not be right customers for your product. Instead why not build some other content like whitepapers, video, presentation, etc. that a prospect might be willing to sign up for. That will give you better qualified leads.
I help B2B clients build their product marketing strategies. Happy to chat if you have more questions.

We have used PopupDomination as it signs people up to a newsletter.... so if you need a conversion tool, I'd suggest integrating it with FeedBlitz.com and signing them up to an Autoresponder email series which helps them gauge if your product suits their needs

For more on Autoresponders and how to write them and integrate them into your marketing
http://creativeagencysecrets.com/your-guide-to-autoresponders/

PLEASE SAY NOOOOOOOOOOOOOOOOOOOOOOOOO TO POPUPS!!! (a thousand tiny babies are weeping at the sound of your nonsense).

Why not buy a hammer and go around and pound people in the knee cap until they buy from you? That's just about as awesome as using popup.

Here's a better plan -- be so bad ass that people automatically want to get in bed with you. They're asking for your details, huh? How about that?

Well, I'm not a huge fan of popups myself - BUT - being in business you have to try different things to see what works for your business and your target market.

Popups DO work, unfortunately. Data proves it. Yes, they are annoying to some people - note many people who might get annoyed with popups have marketing knowledge to some extent - regular folks don't find it that annoying.

Dan Zarrella tested popups and found that bounce rate remains the same pretty much, but subscription rate goes up a lot. Judge for yourself
http://danzarrella.com/my-data-shows-email-popups-work-and-dont-hurt.html#

Am I advocating for the use of popup? No, I'm advocating for understanding your business objectives and knowing your target market. If popup helps you achieve your business objectives without upsetting your target market, than go install a popup and get subscribers.

Make sure your offer is superb, and don't spam them with sales emails once they sign up. Respect the subscriber and their inbox. Deliver value!

As for services, these are some of the popular ones:
- https://optinmonster.com/
- http://pippity.com/
- http://popupdomination.com/
- http://ninjapopups.net/

Just a few to name and check out. Optinmonster has great, easy on the eye optin popups.

Remember, TEST, TEST, TEST. If it doesn't work, great. You know it doesn't work. Don't just take people's naysaying and roll with it. They mean it well, but testing is key!

Its probably wiser to use a welcomegate versus popups especially as popups break on mobile devices

Your original question is pretty vague, if you're looking to build a list and use that list to convert prospects then yes that strategy may work but as other posters have mentioned, a tactic like this is not going to do anything for conversion unless it fits well into the broader marketing strategy

There is several software that can help you out when it come to pop-ups. You can check this link for further information: https://www.g2.com/categories/pop-up-builder
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath