I just used MP3 Splitter for the first time and while it definitely splits MP3's my problem is it's not very accurate.
Now admittedly I'm using it to trim multiple hour files but when I say I want a two hour section, it can't comply. I get random size chunks. Oh well. I haven't tried it on a standard size music MP3 yet.
I've used this splitter for years. It has a simple, intuitive interface. It will split only mp3 files, to my knowledge; but it has handled, and quickly split every file no matter the size.
MP3 Splitter only splits two ways. First a file can be split into a number of equal pieces. Secondly a file can be split into pieces of a specified length.
If you're looking for a simple straight forward splitter, I recommend this one.
I have not used the 'joiner' portion of this utility.