This application offers you more than its name suggests. Not only the program lets you convert MKV files to other formats, but it also enables you to export AVI, MP4 or MOV videos to files with different extensions, extract soundtracks from clips, create photo slideshows, and much more.
If you tried converters from the same developer you'll notice a resemblance between those apps' main windows and the interface of MacX Free MKV Video Converter. On the left side of the screen you add the videos you wish to convert and on the right side you can preview the input files.
Even though the application features a large list of output formats, you can convert clips to only a couple of the profiles, like MKV, MP4, MOV, AVI, FLV, MP3, AC3, OGG, and PNG. You need to download and install MacX Video Converter Pro to be able to convert videos to all other output formats.
In my testing, I selected MKV and MP4 videos as input files and chose AVI and MP3 as output formats (cropped the MKV file and trimmed the MP4 video). The app didn't took too long to offer me the results I needed and the output quality was all right.
All in all, if you can ignore the fact that you cannot convert your videos to all presented output formats, I'd say it's worth trying this Mac utility. Otherwise, I'd suggest you try MacX Video Converter Pro which supports a lot more output formats and comes with a reasonable price.