If you do mount only a front brake, I do recommend actually using it regularly, not only for emergencies, so that you are familiar with it and dont flip over your bike - might leave you worse off than if you had just slowed down as much as you could backpedalling/skidding.
If you don't care much for aesthetics and decide to mount a brake, you might as well just mount front and rear, most come in sets anyways.
If you do mount only a front brake, I do recommend actually using it regularly, not only for emergencies, so that you are familiar with it and dont flip over your bike - might leave you worse off than if you had just slowed down as much as you could backpedalling/skidding.
If you don't care much for aesthetics and decide to mount a brake, you might as well just mount front and rear, most come in sets anyways.