I use a Braun series 9 on my head, at most every other day but often leave it for 3 or 4 days. I also use a safety razor with just hot water to cut a straight line at the top of my sideburns.
I've used a safety razor on both my head and face. I found the best way to get a really close shave was to tense the skin to get it as flat as possible in patches then shave that. Do a first pass with shaving butter and then go over it again with just hot water in slow long strokes until you feel your skin smoothen.
I have sensitive skin and the second pass would cause some irritation but using a good moisturiser (I use CeraVe) after helped a lot.