I've got two 1588 Hovabators with egg turners. I've had a lot of problems hatching but honesty it's probably got less to do with the incubators and more to do with fertility and our altitude. Once you get the temperature set it stays stable, just maybe not accurate. There's no humidity controls but it holds the humidity well. The stability depends on what % you go for. The wells in the bottom hold water for a few days, the humidity holds stable as long as there is water in them. Even with the smallest well I can't get below 40% so I usually don't use them till lockdown.
I've done 3 hatches so far this year. Though my hatches have improved they are still not what I would call great. The thing that has had the biggest impact between my first hatches a couple years ago and now has been switching to dry incubation. Now that Spring is here, and hopefully no more really cold days that kill eggs, I'm hoping for better results. Though after chatting with a silkie breeder, I'm wondering if I'll ever get anything really good. She seemed happy to get 40% and the way she made it sound that was normal around here.