If I try to generate a longer chapter, about 30 minutes to hour or so, there is no protection that could let user avoid generation of two files with the same content, and of course the charge is still double. Also, there is no visible confirmation that the click was registered (the button does no change the caption or color etc.). Because of the length of the chapters, a few mistakes like that can can a few bucks which is unfortunate.
If I try to generate a longer chapter, about 30 minutes to hour or so, there is no protection that could let user avoid generation of two files with the same content, and of course the charge is still double. Also, there is no visible confirmation that the click was registered (the button does no change the caption or color etc.). Because of the length of the chapters, a few mistakes like that can can a few bucks which is unfortunate.