Those fans aren't panaflos. They are NMB 3610KL-04W-B40. This is a 2850rpm 92mm fan rated at 50.8cfm and 34dBA. I have two of them fitted to the back of my Chieftec tower and they do a fine job. They have a bit of a noise to them, but not bad for the air volume delivered. I bought the wire grills on mine, adds 20 cents making it a 59 cent assembly. The grills are attached with those nifty little plastic button retainers. They are very high quality fans. They are perhaps one speed grade higher than I would normally use, a flaw easily excused considering the economy involved.
this thread is kind of old now, but for those of you who bought these 39cent wonders (i got 15) if you want rpm monitering the fans support them. if you pull the label off of the back you will see a third solder point next to the 12v and ground, i hooked up one fan and used a wire to touch that third lead to the fan rpm sensor on one of my computers and it reports at ~2850rpms.