27MHz FM radio control crystals are a niche product now, most "serious hobbyist" RC cars/boats/planes/drones are controlled with 2.4GHz channel-hopping equipment, more sophisticated but generally much cheaper than older <100MHz and UHF equipment. I bought these crystals for "legacy" control systems that can control submersibles at some short range, 2.4GHz doesn't penetrate or propagate in water. I'm relieved that I was able to find these crystals to make my project possible.