The Otterbox Defender case for the original Kindle Fire weighed 9.76 oz. So, this would weight a little more than that due to the increase in size. Essentially it's going to add at least 50% more weight to your Kindle Fire HD 8.9" since the tablet weighs 20 oz.
the best way to see how this is done is to look at the video on youtube, the video will actually walk you through it step by step. type in the below statement and the link will pop up on youtube.
otterbox kindle fire 8.9 care instruction
It is my son's Kindle. While I have used it I use it sparingly. My son, on the other hand, has very little patience (again, he is 4) for things not going the right way. I am confident if there were a problem during his drawing and game play he would have mentioned it. I did, just now, give t a quick test and it seems to respond without error. I do hope this helps :-)