I use HBN on my long range rigs. After using it for a couple years, I have not seen any issues with inconsistency as long as you keep your process the same. If you change the way/amount of time/amount of HBN used, then yes you see some changes. The simple way to avoid that is to do it the same. I also try to coat my bullets in large lots to reduce any possibility of inconsistencies.
I had some rounds that had been stored about a year that I intentionally didn't coat, of the same caliber and same bullet in the same box with bullets that I did coat. Wanted to see if bullet weld was in fact an issue, and adjusted my die .050" deeper. Nearly all of the uncoated bullets had a loud "pop" when seated deeper, and the seating stem actually slightly dented the bullet, and they weren't consistently seated due to differences in how much the bullet was dented by the stem. To get the same CBTO, I would have had to slightly adjusted it for each individual round. All the HBN coated bullets seated deeper just like they were being newly seated in the case, and all seated to the same CBTO. That is exactly the reason why I started HBN coating, to keep consistency. Just make sure you don't store your ammo somewhere like in a truck or anywhere that it will be vibrating, it can cause the powder to break down and changes pressure significantly.
There is a significant pressure drop with the same charge from coating bullets, I usually have to add 1-2 grains in cartridges like a 6.5x284 up to 7mm rem mag to reach the same velocity, but I have noticed you can get around 20-50 fps more velocity prior to seeing the same pressure signs as with a naked bullet. That isn't much, and is not the reason I coat. Another thing I noticed, at least with the 147's in my .260ai and 180 VLD's in my cousins 7mm rem mag, was that it brought e.s.'s and s.d.'s down. Other guns I have used it in (.338 NM, .264 wm) have always used HBN, so I don't have a basis of comparison for them.
I have heard about it increasing barrel life, but there isn't really a scientific method to test this, as two different barrels made by the same manufacturer one after another may wear differently. However, I can see where it could due to a lower coefficient of friction in the barrel, though I don't know if that would be offset by the slightly higher powder charge that is needed to reach the same velocities.
My main reason for using it - shelf life of consistent ammunition, and increased consistency of said ammunition.
Also, not sure why but I don't see an option to vote on your poll.