I am in the same boat as my two girls won't eat pea flakes and I've also tried two different brands. The first brand wasn't very good, being in little bitty pieces and didn't seem very fresh. But the second brand, you can clearly see it was a flattened pea and nice green color. With both brands, after not being successful with hand feeding, I ended up sprinkling the pea flakes into the pellets. My hope was they would accidentally eat it and discover how wonderful pea flakes are. However, every time I do that, the next morning I find the piggies ate all the pellets but left the pea flakes behind.
I met another guinea pig parent through NextDoor and I gave some for his piggies to try. They like it, so I will give the rest of the bag to those piggies. End of my pea flake experiment.