MP3 Trimmer is a Mac utility designed to help you easily extract segments from your MP3 files. The program is packed with a straightforward interface, gives you access to a couple of audio effects, and provides you with quality output files.
All you need to do is to import your MP3 file, select the segment you wish to extract, add audio effects if needed, and export the resulting file to your local directories. The program will immediately complete the given task, without slowing down your Mac.
In my testing, the program occasionally ran slow, especially when importing and exporting files. However, this doesn't mean that it's the tool's fault; it could happen because of my Mac as well.
Another aspect you need to consider before buying this utility is the fact that you can find cheaper solutions. For example, you can use Mac's QuickTime tool (import the MP3 file, hit the Command+T keys, and select the segment you wish to trim). Still, QuickTime doesn't provide you with audio effects (for instance, Fade In and Out effects).
Hence, it's up to you to decide, based on your needs, if it's worth purchasing this audio tool for your Mac or not.