Question

Electric trimmer and wife.

The price of my haircut also comes with a cleanup too. So I go haircut once every 4 weeks and neckline cleanup every two. If just doing the neckline there are plenty of good trimmers that you can maybe get a buddy or spouse to do it for you.

I just have my wife do it with an electric trimmer. No need to have it "razor blade close".

+1

Wall mounted mirror and my trusted Blackbird on a weekly basis.

I shave my head, every day, so I am not certain if my suggestion would help, but you can always try the suggestion mentioned above; use a mirror with one of your mild razors. It isn't as difficult as it may seem.

Electric trimmer

Been cutting my own hair for well over 20 years (electric clippers and scissors), so part of that routine is trimming the neck hair, as well.

Obviously, a muscle memory has developed over all this time. The interesting thing is that it has translated to using a DE/SE razor, so sometimes I use my razor on my neck in between haircuts. (Silly but effective do-it-yourself tip: To get a straight line back there when using clippers, use a long piece of masking tape or a rubber band.)

This is pretty much my routine, as well.(except the masking tape or rubber band to keep the line straight in back. Great tip, Matthew!)

... use a mirror with one of your mild razors. It isn't as difficult as it may seem.

+1
I use my Feather Popular to clean up the back of my neck with whatever lather is up for the day.  Easy and painless.

Inbetween haircuts, which are about 2 weeks, i take beard clippers and just clean up my neckline. The hair is just long enough to come off with ease and there's no need for a razor or lather

I do the same thing, but with a Bic Metal. The neck hair is fine enough that I don’t need soap, so I shave the back of my neck simply wet.

Cheers, Steve

I lather further back on the first pass and just reach with the DE razor, just the one pass. I can pretty much get to the middle of my neck. I keep my hair pretty short so its not hard. I've never cut myself back there. At least not that I've noticed