Do I need a cement mixer?

Well. mixing concrete by hand is, as stated in our 'five interesting facts about concrete', a very  laborious and time consuming business, and it can go horribly wrong. 

To be honest, if you are thinking of building a shed, laying down foundations for an out-building or any other building on your property and you want to speed up the concrete making process by a large margin, then a cement mixer is an affordable, labour saving device.