Pros: Inexpensive, available, holds temps fairly well.
Cons: Light weight construction, difficult to clean all portions. Less stable temperature than forced air.
First off, let me say that I am a licensed poultry technician, with many many years of incubation experience, with chickens, guinea fowl and most recently, Emu.
I have used the Little Giant incubators with great success and I believe they are a good choice for the novice or someone who will only hatch a few times a year.
These incubators are Styrofoam, which as most people are familiar with in coolers, which makes them hold temperatures Very Well! Adjustment and calibration is very easy for the beginner and once set, there is very little need for fine tuning of the unit. Still air units are just that, reliant on the air being "still", this produces strata of temperatures inside the unit, say 102 deg. F at the top of the egg, down to 97 at the unit floor.
There is also pretty good visibility through the Plexiglas top panels. So, if you're doing a class project and want children to see into the incubator, this one is ok for that also.
Without the forced air add-on, this unit is very temperamental in a room where temperatures may shift dramatically. If the room is kept at a constant temperature, say between 68-80 Degrees F., the still air unit is ok. Because of the still air aspect inside the unit, it relies on air being very stable, a slight breeze will affect temperature. It is the normal rise of heat, which draws new air into the unit and exhausts through small holes in the top. This is to be controlled by little red plastic plugs.
Styrofoam, is indeed porous and also will not stand up to too much abuse by the user. The basin (bottom portion) is also the place for water, which increases humidity during hatch and incubation. A sanitizer like Tek-Trol, commonly used in the poultry industry, can actually eat through the bottom, leaving it porous and unable to hold water without allowing it to leak through.
IF you use the automatic turner, it must be removed when chicks begin to pip/hatch. The turner holds more eggs than may be reasonably hatched on the bottom galvanized hardware cloth/screen. So, you're counting on eggs not making it, to reduce the number by the time hatching occurs.
Also, with such a porous surface on the interior and all the exposed components, cleaning after a hatch has occurred, is a chore. There are sprays, but be careful, they may attack the plastic windows and also the sensitive Styrofoam.
Please don't misunderstand my review. I DO endorse the use of Little Giant incubators and find them very dependable and economical. Excellent for class room use!
Recommendations: Get the Little Giant with all the extras... 1) forced air unit 2) automatic turner 3) plastic tray to protect the bottom of the unit, this tray holds the water and is easily cleaned. 4) the little giant and Brower top hatch incubators are both demonstrated in a DVD Titled: Regarding Chickens. Take the guess work out of incubator use and review that DVD. Or get a book titled Chickens in your Back Yard for written details on incubation practices. Both well worth the headache you'll save.