I haven't come across one that works smoothly on it yet, mobile devices just work differently than desktop sites

Well, since you're going down the road of pop-ups, at least set them so once a person clicks "X", they don't show up in the future.

I always recommend people to ditch pop-ups because they force people to give their emails. And many just enter bogus email addresses just to make that thing go away. Plus, some visitors get annoyed and leave the website, never to return again.

It's true, pop-ups generate bigger lists, but bigger doesn't necessarily mean better when it comes to email lists. I'd rather have a list of people who opted in without me pushing them too much, rather than people who couldn't read my website if they didn't sign up.