So Im looking at getting a P4 upgrading from P3S. Should I just fly it right out of the box without updating firmware and see how it goes? I dont want one of those horror stories I see posted with issues after updating the firmware. Advice please! ( Have not yet bought the P4)

Hi. This is a question which polarises many, so you'll need to make your own call based on how risk adverse you are.

I am personally of the view that firmware updates are made available for a reason, so will always update when they are released. It's true that some collateral bad code may be released occasionally, or ever that the FW may be corrupted when applying to the craft, but generally that'll be obvious fairly quickly and you have the ability to downgrade if that issue affects you. I've yet to read of a catastrophic issue introduced by a FW update, such as an instruction to 'stop the motors and explode on impact with the ground' being programmed into the RTH button. It's worth also keeping in mind that the P4 FW is now reasonably mature.

So, if you were asking me - yes, upgrade. My only suggestions are to update via Assistant 2, and as soon as the craft is powered on and detected by the app.

I would fly it as it is out of the box first to check everything works. Then when you are familiar with it, update the firmware. You have the option to revert back to the previous version if you don't like it.

I have 4 different DJI birds....
I have performed various DJI  updates upwards of 20+ times.
Honestly for me the only time I had an issue was once when I lost battery power on a P3A during the update process.
Even then it was only a matter of performing a reset and listening to 15 minutes of annoying beeping until the update restarted, at which point it installed successfully and I was back in the game.
I have never experienced a dangerous situation or gross malfunction due to an update.. a few minor bugs here and there,  but those are usually remedied fairly quickly.
If this is for personal use .....then fly the bird and get to know it... if it has a few glitches you do not like, then try an update.
If this is for commercial use.... then keep you're bird up to date and note the date and version numbers that  were installed. If nothing else the FAA will consider this Proper CRM to ensure air worthiness.