Maybe they do it to look the cheapest so when you phone you think you getting the cheapest but then they hit you with an extra £295 for the head of your choice, you already on the phone so they hope you carry on with the order - even though now they are not the cheapest.
Also there are 4 heads to choose from, all the same price, so if they wanted they could advertise at the head included price but add "includes one head of your choice".