The first difference between the Ovation 28 EX and the Rcom 20 Max and Pro is the egg capacity. The Ovation 28 holds more eggs; up to 28 hen-sized eggs or equivalent. The Rcom 20 Max and Pro models can hold up to 20 hen-sized eggs, or equivalent.
The Ovation 28 EX, the Rcom 20 Max and the Rcom 20 Pro all have a humidity display and automatic humidity control. But, the type of control is different as the Ovation uses a pumping system whereas the Rcom 20 Max and Pro both use a heated water humidification unit instead, giving them more precise control.
Finally, the Rcom 20 Pro has a ‘species selector’ feature and specific settings for egg-turning; both of which are unavailable on the Ovation 28 EX.