As far as 30 fps vs. 9 fps video rates are concerned, why use one over the other?

Thermal cameras operating at 60 fps and/or 30 fps (NTSC) or 50 / 25 fps (PAL) video rates are export-controlled by the U.S. government.

FLIR's OEM camera modules — including Tau2 640 (both 60 and 30 fps), Tau2 336, Tau2 324, Quark2 336 and Muon 336 — are classified as dual-use items and require export licenses from the U.S. Department of Commerce.

The FLIR Vue and Vue Pro (640 and 336) are also dual-use.

The U.S. government allows thermal cameras with frame rates less that 9 fps to be exported without a license. This is why FLIR offers thermal cameras with "fast video" and "slow video" options.

Quark2 640 (both 60 and 30 fps), and Muon 640 are controlled to the ITAR, and require export licenses from the U.S. Department of State prior to delivery outside of the U.S. or Canada.