Since I have never seen any GPH water movement chart for the Matlala diffusers, I'd check the water temp from top to bottom in the pond once it's running for 10 days to see that there is only a few degrees difference in water temp. That will let you know if they are moving enough of the water up to the surface.
I can report about this.
Visually, the Matala diffusers move an amazing amount of water. And I have done temperature readings, which were as concerning as you could imagine, heat wise. During a long hot stretch of weather, I paddled around and took temp readings, compared top to bottom data, and found no more than 2 degrees difference from the 11 foot deep holes where the Matala were located, and top water, 1 degree in some spots.
Temperatures were taken with a Fluke meter, K style thermocouple on a long wire with a clip on sinker.
The findings, along with Bob Lusk's article on the thermocline topic, motivated me to move the diffusers up a couple feet, where they remain.