RE: Futaba High Band / Low Band
The issue is with reduced range. Receivers are tuned for a specific frequency or band of frequencies and the further from that frequency the crystal, the worse the reception. Think of turning the dial on an analog AM/FM radio; the closer you get to the actual frequency of the radio station, the clearer the signal. Futaba receivers are tuned for the middle of the low or high bands; around channel 22 for low band and channel 47 for high.
If you're flying helicopters, park flyers or other aircraft at close range it won't be much of a problem. The range of a properly tuned radio/receiver system can be more than a mile; well outside the limits of visual recognition. So if you're not too far off frequency, the reduction in range won't be that significant.
FYI: I recently sent a crashed low band with a channel 16 crystal to Futaba for repair. When they repaired it, they tuned it for a much narrower band; specifically for channel 16; and suggested that if I changed crystals, not to go more than +/- 3 channels from 16.
Keith