I use a DE razor with a SB although I have used SE and OC combs as well. The only slight challenge is navigating some of the more concave parts of the armpit, but I find it very safe. I have used an electric trimmer in the past, but the results aren't as long lasting. I do have a dedicated brush although mainly for convenience. Definitely not a weird question.Shave with a blade, wow. Do you have a dedicated brush? Is that a weird question?
Just one other thought: It seems that many women also shave their armpits on a probably more regular basis than men, with some form of razor. Thinking about it now, there is probably a whole wealth of information on shaving technique for that area.