The benefit is that if an egg goes bad you can remove it.

The benefit to a lid on the egg tub is that you have much finer control over the humidity and after you open the incubator the eggs will return to the right temp and humidity faster if the moisture is contained.

Sure, there are plenty of different ways to incubate. Professional breeders have worked out the kinks on this over the last 50+ years. There is no real reason or need to re-invent the wheel on this one. The total cost of a DIY incubator with tubs and substrate is under 100 bucks. If you're trying to work around that cost, consider that the babies will consume that much in food and bedding in their first month or two.