Why not add WHERE they commute. Single speed or Fixed where it is flat is a LOT easier then hilly areas.

I'm still toying with making a set of "his an her's" single speeds (wife is use to grip shifts on a MTB not stem or down tube. I'm trying to warm her to drop bars and not ready to drop the coin on a bike with STI till I'm sure she is going to stick with it) for the rails to trail mup we ride. Mostly this is to slow me down to her speed. I averaged 15mph on a hilly metric 2 weeks ago. She runs along about 10mph on the flat Mup.

I have experimented with sticking too just one gear on my commute and weekend rides trying to figure out what gear to buy but I have a couple real booger hills on the way that would just plain suck on a 16(17)-40 gear selection of the bike I am thinking of converting. My touring bike that I commute with I am usually pumping 18-36 on the one hill.