Aiseesoft MKV Converter for Mac is a commercial video converter. It allows you to convert video files into different formats. Although the format "MKV" is mentioned in this application's name, that doesn't mean that the app is a dedicated MKV converter or that it has any special features for the conversion of those files. It is more of a multi-purpose video converter. That doesn't either mean that this is a bad converter. In fact, it is a very good one, and it can produce high quality files very quickly.
I tested the application by loading a few MKV files that I use for testing converters. Those files had multiple audio and subtitle tracks. The application failed to detect the subtitle tracks on both files. So, you can't save the subtitles from your MKV files, if that is what you are looking for. Also, when you want to convert to MKV, you can't choose a subtitle file or multiple audio tracks either, which is why I say this is not an MKV converter.
As a normal video converter, the app is fully-featured. It comes with a nice trimmer, great format support and the conversion engine is fast and it can output great quality files.