Some people love the CPM machine. Others hate it.
Some surgeons recommend using it and some don't.
While using a CPM does seem to help in the early days, it makes no difference to your recovery or ROM in the long term.
So, if your surgeon recommends it and you like it, use it. Don't worry if you don't like it. Not using it won't affect your outcome.
If your surgeon doesn't recommend it, don't worry, because you'll still get there without it.