I like the sensor because it has the ability to prevent you from running so low that you drain the wormdrive and going through another initial firing process. However, because of where the sensor sits in the hopper, and how the pellets never fall directly to create a perfect pile under the sensor it constantly tells me im low when really it is just that part of the hopper that is low. In reality, the pellet level will triple when you shift the pellets around. The hopper needs to be designed so that the pellets fall orderly. 9 time out of ten it sends you false alarm warnings, but it could help during long smoking sessions for, say, a brisket. Worth the 80 bucks, but could be improved.
If you get a Wifire grill you need to make the extra investment for the sensor... especially if you plan to cook meat for long hours as the feeder cam have pellets that stop feeding due to angle in the box.
I needed a sensor because I once ran out of pellets, and since then I have been kind of obsessed with pellet level. Now I do not have to worry since my app tells me when I need to add pellets. The reason I did not give it 5 stars is that, even after calibrating, the level indication is really not accurate. When the hopper is 80% full, the app says ~40%. I just am thankful that it is erring on the conservative side, so I add pellets earlier than desirable, rather than after running out of them. Even with the accuracy problem, which others have also noted, I feel it is a necessary addition to my Traeger Pro 575. I recommend it for the peace of mind it gives me.