Does a good job of reducing file sizes, but I've encountered several instance where it won't complete its task, indefinitely showing the cog icon next to the images being processed.
Also, the dev, for some reason best known to himself, has decided to allow the Sparkle updater to download updates without user consent, and without offering a user-facing option allowing the user to disable it. Out of the dozen or more apps I have that use the Sparkle framework, this is the only one to be so coded. After conversing with him by email and presenting what I thought were good reasons to include such a feature, the dev still refuses to do so.
Hence, only 3 stars.