Agree with opinion using your own bat vs a different bat,
some are top heavy, thick handle vs thin, etc.
Seems like an advantage if you happen to use the tester's choice brand.
Think a real measure is what bat a player uses in a game, otherwise not really your bat speed.
Personal experience:
Son was 3-5 miles faster with his own bat (wood).
Never saw anyone use BESR for testing but was not looking,
we sold all son's old BESR bats to a dad down south when bat rules changed.