Comp Title Giveaways to Grow Email List- Viable Strategy?

I don't have any books published yet, but I'm working to grow my email list before pitching the ones I've written to an agent.

I wrote a second children's story in the same world, intending to use it as a reader magnet, but now it's a companion story that belongs to the series, rather than just a teaser. Now I'm not sure what to do. Do I give my best work away for free, before I have something to sell? Is that being faithful in the little things, or casting my pearls before swine?

I'm considering an alternative strategy of organizing giveaways of comp titles, both stylistic and thematic. I've listened to Thomas' episode with Kelly Jo Wilson, and I want to again, but I'd love to hear from any of you who have successfully grown your email list with giveaways, especially before you were published. Do you have any tips or cautions to share? Did you run any other promos/ publicity simultaneously? E.g. podcast interviews, Facebook ads, etc?