I hatched 3 clutches of my first ball python eggs this summer without any problems.
I used the NON-FAN model, blocked OFF all the air-holes with clear-packing tape (kept drying out). Lifted the lid every few days to allow air-exchange.
I did use a Helix DPS-1000 thermostat. I just turned the built in waffer up high enough so it does not kick off before the Helix controller keeps the temps at a steady 89.
Some Helix's run a little hotter or cooler. One of mine in the same ROOM right next to the other incubator ran at 88.5, were the other one ran at 89.5.
But I still had lots of luck using them for the first time, all 3 clutches hatched. Only lost one egg from a total of 17 eggs (3 seperate clutches)