I just received the small one in the picture on the left. Tried out a Z2 workout with just that one pointed at my face inside with temperature about 19C/66F, and I was sweating just a little bit by the end. So I need more, but I was very impressed with the low noise and the concentrated amount of air it produces, I could still understand the movie I was watching on the iPad in front of me. I have now ordered big brother on the right, according to the specs that one should give out 6x more air!
for people in the EU, here are the links on amazon: