It seems to work so far, although I only just installed it. Used the Generate Thumbnails option under settings to have it work on existing posts. Seems to be fine, and it retrieved the images correctly even though they are posted by URL from Smugmug. I'm satisfied.
Seriously, why isn't this part of the core WordPress code? The default Featured Image option sucks because it doesn't work with images posted by URL (and doesn't even give you an error message).