The problem is that FPV is probably illegal everywhere (regardless of the frequencies) -- if you dig deep enough.
One advantage of the little 5.8GHz modules I'm using is that they're not on the same frequencies that 5.8GHz routers and cordless phones are using so you're less likely to encounter (or cause) interference. And, given that we're talking minute amounts of power that are quickly absorbed by the environment, it's rather unlikely your FPV transmitter will interfere with anything else outside a 750m radius.
I certainly believe that we ought to observe the law but i also believe that pragmatism and commonsense would make laws unnecessary in the first place.
Some of the poor guys in Europe have no chance of doing any FPV because the restrictions on their bands are so massive that they're limited to just a few mW on the 5.8GHz band and not much on anything else.
However, despite the fact that so many people are obviously flying FPV (illegally), there have been no reported incidents or issues with the use of this gear. That (to me) indicates that our tiny, low-powered transmitters aren't a threat to existing services on the bands where they're used.
Having said that -- i would never contemplate seriously using some of the 900MHz band because around here, some of it is used for GSM phones and the rest is for aircraft navigation systems. I don't want to lose my video signal to someone sending an SMS and I don't want to be responsible for a commercial airliner plunging into the ocean somewhere.
From that perspective, I believe 5.8GHz is the most suitable band for FPV for a number of reasons:
1. the gear is small and light
2. the range is automatically limited by the environment so potential for affecting other services is minimal
3. in most countries, 5.8GHz is used for radiolocation, amateur or fixed satellite communications so is unlikely to clash with FPV use.
4. 5.8GHz FPV transmitters tend to be of limited power (200mW-500mW) so has limited potential to interfere with other users of this part of the RF spectrum.
Also, in most cases (wireless LAN aside), 5.8GHz systems tend to be used with highly directional antennas which means that the potential for interference between FPV and other services is even more limited.
I'm not advocating that people break the law -- but I am saying that with careful, commonsense attitudes and practices, the potential for any conflict with other services on this band is very, very low -- as has been proven by the number of people already using this gear without "the powers that be" or other users of the same band even knowing that such use is going on.
RCModelReviews.com, just the facts.