For Kindle devices the mobi file is the one that you will want to use. Just plug your Kindle into your computer via USB and transfer it over. The epub version will be better for iPads, smart phones and tablets.
I have had many questions about when the book will be available in the Amazon Kindle store. Due to reasons beyond my control (their absurdly limited payment options for Kindle publishers to begin with) it is not currently on there. I will continue trying to work out a solution with them though.
If you are a previous buyer and want the mobi or epub versions please just email me at firstname.lastname@example.org and I will send them to you. Thank you for all the patience!