I have a 1588. It is styrofoam, not plastic. I don't have any trouble with it holding temperature or humidity, as long as I keep it in a stable environment. The fact that it is forced air is really nice as opposed to a still air, but that is not exclusive to a 1588. Mine has five different reservoirs in it so you can play with the humidity by filling different reservoirs, but it is hard to tell how full those reservoirs are when the lid is on.
Mine only has one vent hole. I'd prefer two. I'd like the extra flexibility in bleeding humidity off if it gets too high. I put a few straws with those flexible accordian joints together and can reach all the reservoirs to add water without raising the lid during lockdown. A second vent hole would make that easier though. And I would be able to leave my thermometer in full time if I had a second vent hole without worrying about ventilation.
The window at the top is not real open. The fan and heater blocks a lot of the vision. It is kind of hard to see the eggs right in the middle of the incubator because of that.
In guess my biggest complain is that with it being styrofoam, it is a little hard to clean and sterilize after a hatch. The water reservoirs in the bottom are in a plastic insert. You can remove that and clean that, so that makes clean-up a lot easier, but those chicks roaming around do get some stuff on the styrofoam sides. If you were just using it as an incubator and had a separate hatcher, clean-up would be easier.
I usually only use it twice a year. My 1588 is good enough for that. But if you plan on hatching fairly regularly, I'd suggest one that is easier to clean. I do recommend the turner whichever you get.