Hi!
Agree!
I well trimmed trimmed airplane doesn't need any mixes or to fly straight at any speed!
A trimmed airplane remains in forward flight with just slight elevator input.

Remember that a model airplane should always be trimmed at full throttle/speed so that plane flies in a stright line ....and trimmed (by changing the Cof G) so that it remains flying in a straight line, without loosing too much height, at nearly every throttle setting!