Understanding why a good incubator can be worth the investment in time and money. Commercially available hobby-specific incubators are available, but building your own can be better and less expensive. Some hobbyists work with more than one species requiring different temperatures and humidity. Space is also an issue, the commercial reptile incubators are small but can be adapted to do the job. The cost for several temperatures/species by building your own can be much less.
I'll describe how to build your own incubator from start to finish, as I have done and studied many homemade and commercial styles. I'm using a small glass door refrigerator and this is best for me. Some simple designs are good and can do the job, foam coolers and glass tanks with insulation, modified reptile, laboratory and bird egg .
I've used just regular deli cups for mantis ooths as many do with some success. A percentage of ooths wont hatch of course. I've witnessed females mating and laying oothecas feeling fertility was certain though unsuccessful with hatch. There can be many reasons for this like wrong incubating conditions, either parent too old or fertility issues just like other animal and humans. Simple minds and some critics may just think you did something wrong and that may be the issue. Mold, mites, parasitic wasps, humidity, temperature are factors. Whether wild or captive bred a fertile ooth can die or be damaged. I this in more depth in different chapter of my book "Mantids for Dummies".
Ooths are to a point "adaptable" naturally. Varying conditions in nature are normal from season to season of course. The ooth by design will maintain and protect the eggs naturally allowing for dryer hotter or cooler wet weather. and In temperate climates, where adults do not survive the winter the eggs undergo a diapause, hatching in the spring. moisture level depending design, self regulate hatch or results seem less than expected in I started with a glass learned that my time and investment