So, to summarize. There are different batches of serials of P4, and those will react in a different way to this firmware update.
If your P4 is of the batch which faces yaw yaw problem, this firmware will address the issue and fix it.
If your P4 is of the newer batch which mostly do not have this problem, this new firmware will mistakenly overcompensate the glitch and this will result in screwed barometric sensor function, so you very well may overestimate/ underestimate your altitude by dozen of meters. The craft may also ascend or descend by itself by a couple of dozens meters up or down.
Summary: do it on your risk! If it works, DO NOT, I repeat DO NOT upgrade!