I used this plugin on a recent Blogger migration. About 70% of the images said they worked however when I examined the images, they were all 0KB. I discovered my solution by playing around with the code. You need to set an option with CURL to allow it to follow urls redirections. This is done by adding the following code to blogger-image-import.php on line 149. Hopefully this is useful for something else attempting to migrate from Blogger.
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);