The main thing that hacks me off about the biennial flight with an instructor is that, by definition the aircraft must have at least two seats. So I am forced to fly something that bears almost no resemblance to my own machine, other than it has wings and can fly. That might be OK if it was something unusual or exciting but invariably its a C152 or a PA38.
I believe the American biennial, though, can cope with that allowing the single seat pilot to fly their own airplane with observation and instructions by radio from the ground.