As for Leanpub:

1. Last time I checked, they didn't let me take the customer emails and use outside of Leanpub. I find it a very important limitation to the way I do the marketing - via my mailing list. In practice, my readers are more Leanpub customers, not mine. I want to build long-term relationship with my readers, to deliver more value to them, even after they bought my book. To be fair - Leanpub has their own tool for sending emails, I haven't tried that. I'm happy enough with MailChimp, not to see reasons to switch.

2. From the tools I researched, Leanpub is the best when it comes to PDF/mobi/epub generation. It takes a while to learn their process but it was worth it.

3. I'm really grateful that Leanpub allows the process I'm doing - generate the files using their tools, but selling on another site.

Overall, the tools you're choosing should fit your whole process of researching, writing, marketing, selling.