Because it is April, I started a coupon-month to give away my books on LeanPub for less money than the normal price. The URLs of the books already contain the coupons so if you click on them you will be redirected to the right page and can buy the book cheaper.
I would not wait and buy now. When buying you get a PDF, Mobi and E-Pub version, and all future updates (updates can contain new chapters or error corrections). And if you have bought the book you get the new versions without paying any more money.
The coupons end at 30. April 2015