The stuff marketed for women comes in larger quantities because it is held that they have more hair. However, if you are a hairy bloke you can use it on the chesticles as well (but beware of chemicals on the little lower bits and definitely keep it out of the eyes!)
The stuff marketed for men is a little different in that it develops more quickly and it is more expensive. Get the so called "Girlie" stuff and only use half at a time. Measure the constituent fluids then mix; it won't work if you mix up the lot and try to save some mixture. You have to use it straight away after mixing.
Another important tip: use the polythene gloves supplied with the kit or some Marigolds when you apply the mix because otherwise it will stain your hands. The dye does not permanently mark normal skin, but it does affect the thick skin on your fingers and is permanent on your nails.