I don’t ALWAYS agree with Amy, just usually. I use a Styrofoam incubator and am quite happy with it, though it is a little harder to clean than a hard plastic one might be. I think you need to tweak or at least confirm any of them are working properly before you trust them. Calibrate your instruments and run it enough to determine its working right. Don’t trust really valuable eggs the first time either. There is sometimes a learning curve involved.
I generally agree with her on the instructions that came with mine, they were not greatly detailed beyond how to set it up and get it started. They did warn to not trust the thermometer they sent with it, to not trust valuable eggs the first time, and gave suggestions on what water reservoirs to fill when, but they did mention you might have to adjust this based on results. They did not go into how you might have to adjust. I did not spend the money to get the top of the line but since I only incubate two or three times a year my Styrofoam incubator works well for me.