The reason they burn is because they are pulling a fourth of the wiskers out.  They cut the rest at about the height of a day's growth so you will be sure to have to repeat the experience sooner rather then later. 

I've never quite figured out how it was supposed to be "easier"  to run an 8 oz electric over your face ten times trying to get it all gnawed off compared to shaving once or twice over with a disposable which weighs maybe an ounce.  

I can't remember when the last time was that I cut myself shaving....it takes a lot of talent to get a cut  with a sharp safety razor.