What would be more interesting is how many users who have stepped through that process to install the Amazon apps, have then gone on to use the same process to

What would be more interesting is how many users who have stepped through that process to install the Amazon apps, have then gone on to use the same process to sideload malware. This is because it is actually pretty reasonable to make the judgement that Amazon is trustworthy enough to sideload their applications despite the dire warnings, so what you really want to find out is how many people are making unreasonable judgements on what is trustworthy enough to sideload.