Very important to learn and get good at fire control without one first, IMHO.
Don't use it all the time. But it is a blessing for multi-hour cooks for me. Even high heat. I'm often off doing other things and this device allows me to do that with great confidence, just stopping back to check or push the temps a bit. It is really great for peace of mind during these situations. It removes the need to be watching as close to stop the temp rise for example "on the way up". You can dial up/down temps readily without the need to be around fooling or adjusting the vents. Not a big deal normally, but when you are off doing other things it's a blessing.
You still need to master minion, and understand how the tool works. Otherwise you can still have overshoots and all the other problems with fire control if you don't understand all that. It gives a ton of automated control though that helps through all that.
In the end 25 degree swings in temps do not affect anything. But - that said having a device that can/is monitoring and adjusting temps or providing an alarm under certain conditions is helpful for me.
You don't need one, but worth every cent IMHO.
Been usign a Digi Q 2 for several years off and on and would spend that money again.
BTW - just did a high heat brisket yesterday with the ATC, couple days before used it for a rib cook.
Have company over this week/next. Also have to be working and available during the day (day job). The ATC made that effortless and allowed me to cook with confidence while I was juggling all kinds of other stuff not related.
Ribs and brisket came out perfect.
Won't be using the ATC though for the roadside chicken cook though coming up this Thursday
ATC's are a great fire control device. It is though very important to learn fire control without one, and I would recommend doing that first. I still cook primarily without the ATC.
To me digital versions of ATC's have really raised the bar and made these tools both more easy to use and trouble free.