I'm sure your DIY diffusers are very good, although prerecords.com/Diffusor.cfm is an empty domain- you can buy it if you want.
Diffusers are not rocket science, but they are math based, and experience helps as well.
As far as "the best you've found", are you saying you've actually heard or measured these foam diffusers and found them lacking, or is this based on your assumptions.
And concerning the foam ones from Pi Audio, Dave Elledge has told me how he has measured them, how they respond at different frequencies, how different foam densities behave, how paint affects them, how backing board affects them, how spacing affects them.... in other words, real research and experience.