Great tool, thanks. I'm exactly your target audience, one of the many people update extensions one by one, such as by using ExtensionDistributor, without using git.
When I update my extensions one by one, I currently use wget from the command line in Linux and I end up with a .tar.gz file on my filesystem, which I extract. The timestamps on the .tar.gz file and all the corresponding extracted extension files match the 'commit' timestamp for the extension. This is useful to me to provide an audit trail of the updated extension back to the source repository.
In my testing of this tool I'm noticing that the timestamps in the extensions directory all match when the tool was run, not the source repository dates, so I don't have the same audit trail.
Could this tool be changed so the updated extensions (and skins BTW) have timestamps that match the source respository. The curl '--remote-time' option might be helpful.