In my opinion, the grill you bought is great as is and no mods are needed. Probes are also very accurate, and I have no problems at all with the app whether I'm at home or not. Here's more detail on my experience in the month I've owned and experimented with my PB1150PBS.
When I originally tested the temps, I was too impatient and thought the probes should heat up as quickly as the sensor. When they were still 30+ degrees lower than the set temp after 15 minutes, I figured something was wrong, but actually the plug in probes are much thicker and therefore they take more time to get to temp, but they get there and hold it beautifully.
I tried the smoking like a boss heat deflector mod, and my experience was that the deflector caused more of a problem than it solved. Before the deflector, my actual temp was about 30 degrees lower than the display indicated, but after the mod, the actual temp was over 70 degrees higher than the display temp.
I tried the grill two more times with the mod in place, and the problem persisted. After about twenty minutes, the display temp was barely moving, and the interior temp kept on climbing. When I tried to set at 300, the display took forever to get there, and the interior of the grill was 411 degrees. Shut it down, let it cool and tried for 250 on the next attempt. The display reached 250 fairly quickly, but the inside of the grill was at 325 and climbing, so I shut it down, let it cool and removed the mod.
I then set the grill to 250 and put one probe on the left half and one on the right half of the grill and waited about a half hour or so for things to level out. With the display reading 250, I had 248 on the left side probe, 249 on the right, and all temps remained steady. Turns out my grill was perfect right out of the box. No mod needed.
The mod seems to have been helpful for the older model widebody Pit Boss grills, but I can say 100% in no uncertain terms that if you have a new PB1150PS2 with the latest controller, you do not need or want the mod. Here's the readout after the shield was removed.