After mislaying my old Kindle Fire I ordered a new model HD 8. Nice it is larger and the battery life seems to be improved. Of course, there is a learning curve as the operating system is different, but not too difficult to master. Previously I have had several Fires and also several regular Kindles. BUT I have a serious problem with this model. Unlike every other Kindle I have osend, this one will not open any MOBI file other than those downloaded from Amazon. I have called customer service several times and they just can't seem to understand the problem. Simple, if I wanted to have difficulties with formats I could have purchased a tablet from some other company. What i find amazing is the device I now have will not open a file in its native format! Is this some programming goof or is Amazon trying to limit our reading content? I cannot even find a number to contact their HQ or programmers to find out if they are aware of the issue. I just feel isolated and no longer have my friend from Amazon. Bottom line, if you like to read materials from sources other than Amazon DO NOT BUY THIS MODEL.