This thread is likely to get closed down - although the software itself is legal, it’s used almost exclusively for illegal filesharing. The lawyers behind this place are prickley about this, and prefer avoid discussion about it.
And yes, it’s stuffed full of spyware, so will potentially hose your computer.
What Baraqiyal said pretty much covers it. While there is a potential for legal use, it’s far more likely your son simply wants to download “free” music.
it’s also possible to download bad stuff that will screw up your computer, especially if he is interested in getting ahold of “free” software.
Depending on how old he is, it may be time to start monitoring his activities online more closely.