have you taken the time to visit the Celemony website to view the tutorial videos they have posted there? There are lots of good things that will help you figure out the intricacies of this program in those videos. I use ME a lot, but I still learn something new every time I go to look at them....and I've been using ME for many years.
I find that in most cases, I am able to work with notes that are pretty far from the correct pitch and get them to sound right. It takes some effort and time, but that's the price for getting it right. And with little to no artifacts remaining after the edits.
Of course the closer the part is to being right to start with , the easier it is to fix without leaving artifacts.
Another tip: do not use the auto correct function. It often "breaks" things that are not broken to start with.... then you end up having to undo what Editor just did. I learned this the hard way and was having trouble fixing things that were "off" and had artifacts after the auto correct, that were damn close to perfect before the auto correct was run. It's easier and more accurate to work through the track, section by section, fixing as you go only what actually sounds off pitch or time to you, and saving the project after each edit.
Editor and Melodyne in general, are pretty heavy on the CPU. In some computers, that equates to a major CPU draw, and as was the case on my lappy, lots of seeming bugs and crashes. On the DAW however, with more CPU power to begin with, ME runs extremely well and fast...... but I still click save after the big edits...old habits, you know.