The latest model (Released a month ago)
The latest model has the LCD display, diffuse mode and 350-degree oscillation, whereas the HP03 did not have that.
The HP04 is quieter and has 310 litres/sec of airflow compared to the HP03 of 155 litres/sec and 216 litres/sec cool mode.
It is a more updated version of the older one.
Dyson have tested the fans in rooms of 27 square metres and they are designed for any size room, but the bigger the room, the longer it will take to make a difference.
Original PROMOMYER 20% off Sitewide at Myer on eBay Deal Post
I'll wait til they come up with something that works better the larger the room.