it works on very hard distorted guitars yes, but a guitar itself is a very low signal, when putted on a line you just don,t hear anything, and when you do, it has probably a very bad sound, specially at the low end.
so get your self a DI box, it makes the high impedance guitar level, to a studio standard line level of -6db to 4+db. also ofcourse the noise floor is this way much better in balance with the max guitar level. btw you can fit the guitar in a mic input, but it sounds way better over a real di box.
DI boxes dont cos,t you a thing, you get em from 40 euro (45 dollar) new up to 500 euro for like an avalon di
BTW a lot of little mixers, (like the soundcraft compact m4) have also a guitar di input. they cost only 90 euro,s newprice and you also have then 2 stereo line,s and mic inputs to your mpc so this is pricewice and feature wice maybe a better solution for people that need to record a guitar at line level, but would also record more equipment without the needs of reputting cable,s
As you can see, the second mono channel allows the mic input switched to guitar DI level input.