I use the AC Infinity T6 as my inline fan, it's a little bit on the expensive side, but it's temperature controlled with the addition of a digital display if it suits your fancy. For those who want to keep your grow room at a certain temperature, with a automatic shut off once it achieves that temperature, this would be the go to. It processes the hot air it brings in from the outside into cooler air.
I am using the Vivosun 6" 440 CFM Inline it's bit noisy and does not have a display. I am thinking of moving to a AC Infinity CLOUDLINE T4. If you are looking for more on inline fans you can take a look at this site I found they have a ton of great reviews and articles surrounding growing indoors.
A/C Infinity makes some nice,very power conscious fans. Digital controls and 10 speeds. I think the 6" is like 40w and 351cfm at full blast. Price ain't to bad neither. Look at this on eBay CLOUDLINE T6, Inline Booster Duct Fan 6” Cooling Ventilation Exhaust Grow Tents 854759004792 | eBay