In these multi gpu situatiuons a blower is better than a traditional dual fan design, since the blower cooler will move all the hot air out of the case. If, like in the example of the photo you gave us, it were all aftermarket coolers you'd have 4gpus spewing out hot air right next to eachother, so that hot air will very likely end up going back into another card. Basically for single gpu setups you want a two or three fan design, for multiple gpu's packed closely you'd want blowers.