Bloody marvellous things, but you may never see your DH again if he buys one it's a male obsessive thing.
I sometimes get it out when I am feeling particularly vindictive about the state of our house/life/my general existence - very cathartic!
They clean cars, double-glazed windows, patios, sheds, PVC fascias, car ports, mossy fences & walls, plastic garden furniture (not teak, ever!), dustbins, garage doors, garden tools, gutters - you name it, if it's outdoors and filthy, a pressure washer is your best friend.
You must be careful with them (they are really vicious - no mucking about pointing it at the kids, or letting the kids play with it) and you get filthy while using one - old clothes, wellies and a waterproof.
Kaercher are the market leader I suspect and our Kaercher has been very reliable. Make very sure that you get an RCD to prevent electrocution - water and electricity are not best friends.