RE: 250 trex drifting
To answer your one question.
Rate mode is a gyro mode that dampens the rate (amount) of unwanted tail movement.
Heading hold mode is smarter, it not only stops a drift but applies a correction to get it back where it was.
If a helicopter is hovering with its side to the wind a rate mode gyro will sense the drift, correct to make it stop, and then recenter and it will drift again then the gyro will stop it over and over until the nose is into the wind. It will still turn into the wind but at a rate that is manageable by the pilot. (trust me it would be LOTS worse without one!)
A heading hold gyro will sense the drift and instantly correct it, if the wind gets stronger the gyro will apply more correction (as much as it needs right up to the mechanical limit of the tail pitch mechanisim if need be) until it stays put. Even in a changing sideways wind, a heading hold gyro should maintain the nose pointing in the same direction.
This can be clearly seen on the ground with the motor off. In rate mode if you move the rudder stick it will move then center. In heading hold mode it will move and stay there until the heading of the helicopter changes to where it was told to go. Since its sitting on the ground the gyro holds the pitch patiently waiting for it to respond. If you move the stick and hold it there for a few seconds the servo will pull the tail pitch until it cant move it any more.