I never use other people's notes, I am a control freak I prefer my own.
Primarily because than I know that I have read the material, done the work and the notes are written in the way I understand it. Sometimes I might just check with the lecturer on the principles and how I have written something to see whether it is correct.
It is so much easier, although more time consuming when you do it yourself because than you know you know it and further when you have an open book exam you know exactly where it is because you are the person who did the formatting and structure.
As you have obtained a set of substantial notes I would make my own notes and use their notes as possibly a guide or for some additional info or if something is worded a way you understand than I suppose you might copy them into your notes.
Hope this helps.