PhotoSweeper does exactly what it says it does. The description doesn’t sound like hype, just matter of fact. However, once you start using it, you realize that the description is actually understated. There is so much flexibility to find similar photos in many different ways and with varying precision. That last bit is very important. I have lots of photos taken around the same time. They’re similar but not duplicates. I also have lots of edited photos. PhotoSweeper lets me find all the various combinations of similar. And it works perfectly with Lightroom.
As for support, it is excellent. I recently found a case where some dng files converted from older raw files couldn’t be read. While Lightroom read them, Preview and some other apps would not. I sent some samples to Overmacs and a few weeks later received a test version which resolved the problem. Now that’s service!
Update: this latest update includes the fix mentioned above. As well, it includes support for the raw files from my new camera, just like Lightroom.