It's difficult to find the "Download" button.
Amazon has a "one click" to lessen user action to purchase an item, MarketPlace is requiring to many clicks to download a file. I think users will also get confused when they see the "purchase" radio button because they think they're download a "free" software. This is another reason to go with "$0.00" instead of "free" because with $0.00, users will know that they have to "purchase" it but it's going to cost $0.00. With "free", it's confusing when the "purchase" page comes up.
Another alternative is to skip the purchase page when the plugin is "free" and just go straight to the download page.
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