Using a Guru

I have  had my XLEgg over 15 years. I have smoked, cooked, fried everything but a human. I have never had any trouble keeping the temp where I want it up to 20 hours. Why do so many of you buy those expensive Guru things to keep your egg going. When I get mine at the temp I want, I never mess with it and I can low and slow for many hours without temp change. Does this forum push this product to make money? I watched a young man doing a YouTube video on how to low and slow an butt. All I could think  is what in the hell is all that wiring and probes and stuff just to keep the Egg going. All I do is put my temp probe into the meat, and when it is at the desired temp. I go get the meat. JS