never tried a headblade but my go to for a quick no hassle and very little care needed shave..is a mach 3
i can get a good shave in 10 mins with little fear of cutting myself even against the grain
do you make sure you aren't over-using cartridges? i know its pricey..but honestly for a good safe shave, most dont last for more than 2 - 3 full head shaves.
sometimes it can help to look down as you shave the back of your head, in order to keep the skin stretched tight.
do you have any spots back there? if you catch one of them, that could be the issue.
Also make sure the blade is always moving forward.....what i mean is, if say you dont have a good enough grip and aren't actually firm enough with it, it can slide to the left or the right whilst moving and thats going to cut you