Those were chosen as a quick and relatively inexpensive way to get into low-frequency (about 650 kHz bandwidth), digital RF analysis. My first thoughts were to use a fast SPI controller (e.g., a CLPD), memory (e.g., SDRAM), and a PIC (e.g., 24F or enhanced 16F) for later analysis. I found this introductory link regarding CLPD that seemed "simple" (https://hackaday.com/2008/12/11/how-to-programmable-logic-devices-cpld/ ), but as I read more about that approach, I fear the development time and hidden costs would outweigh the cost advantage.
Given how busy I am this Summer dealing with the devastation caused by the emerald ash borer plus the usual projects, I went ahead and got the PulSAR setup. I did find on the Microchip sites that the 24F can handle that SPI speed.