I use my DE once in a,while. There is always a chance to get a nick with a DE. It's all about the angle, so you have to take your time. The only time I have a problem now is when I lose my concentration. If I have a problem area, I just move on, then at the end I go over it with a regular razor. Congratulations on sticking with the shaving! There is definitely a learning curve when headshaving, especially when using different razors.
The face and neck is harder to shave than the scalp. The face and neck have more contours to it. As for the nicks, I think getting used to the de is important and takes time and patience. I don't get nicks any more but I used to. The neck part is what I always manage to wreck no matter how hard I try.
I learned to shave with a DE , cartridge was not yet invented. Face shaving with a DE is OK not my favorite method, but head shaving with it takes too long and who needs the cuts.