Instapaper users pay to read free articles from the internet in a way that fits into their lives better. Same concept here.

I used it for a couple of weeks. The app is slick and it has some really cool features (like letting you import your own ebooks) but I kept forgetting to open the app and then falling behind. Also the daily reading length of 20 minutes per day felt too long for me, personally.

Ultimately I got it in my head that I'd be more likely to actually read issues if they showed up somewhere that I already had a habit of checking daily (my email inbox), and if the issues were shorter (~10 minutes each) with more fine-grained controls about when they were delivered. So that's what I built!

I actually emailed Michael (the person behind Serial Reader) back in June, hoping to get his blessing to use the word "Serial" in my product's name. Never heard back and eventually I decided to move forward with the name.

I use Sendgrid to send emails, which has worked great so far although it took a while to get my account fully set up.

Re: customers, so far I've had more than 10 and less than 1000. One encouraging sign is that many people are coming back after finishing their first book and buying another.