I have used Chipmunk for about 5 years and highly recommend it. I have used it successfully to search volumes containing over 400,000 files. This took about 20 minutes with the rainbow cursor spinning but it worked.
The only limitation I have encountered is in situations where the duplicate files are located in the same folder. The app finds them but can't delete them itself. They need to be manually deleted.
In these cases, I use TidyUp. This is a much more complicated and versatile app -- but you really need to read the manual!
I recently downloaded Gemini to help me clean up stuff before moving to a new machine. You can download the trial version from their site to try things out and see how it works. It didn't find everything the first run though though, which I thought was a bit odd. I ended up just doing the trial version to find things and then manually reconciling files (the trial won't let you delete stuff from inside the program) which was enough for my short term goals.
Hi, you also could get ED DuplicateFinder from the Mac App store to have a try, it can find files with same content even if those files have different names based on MD5 value checksum algorithm, and now it's on sale.
If you have only a few duplicates, the UI based tools are fine.
In my case I had to clean up my parents mess of 20 years, meaning there were 3+ copies of every photo and probably 100k+ files. Directories were duplicated etc. In this case the UI's were useless and I resorted to rmlint. Be warned: it's not for the average user. But for my use case it was the perfect tool and let me clean up the mess in less than a day.
Again: this is more for people used to compiling/programming in linux.