may wahl cordless came in the post on tuesday finally tested it and gave myself a 3 even wtg came out ok

only hard thing is holding the clipper and looking in the mirror while cutting wtg
You'll get used to it. I usually use just one length attachment, and use the lever adjuster to taper my sides and back. Set it at the middle for this. Then set it at its lowest and hit the outline all while keeping you length guard attachment on. I also use the middle lever setting to hit the sides of my forehead. This will make your cut look cleaner, longer.
After you're done tapering, take off the guard, set the lever to its lowest position and just lightly line it by pressing in the clippers into the back of you're neck while keeping them positioned inward, if that makes sense. "Bite" in the line. After that, clean up all the loose hairs on the back of your neck with it.
You'll probably mess your cut up if you try to get too fancy trying to line it from my experience. Just keep it quick and simple. Takes me less than 15 minutes to chop, taper, and line myself these days.
I got straight hair though, so ymmv.