Burning Blaschak nut here. Haven't tried pea. I don't think my local dealers even carry it. They carry nut for the hand-fired owners and rice for the stoker owners.
What surprises me a little is the range of sizes with the nut. Of course the majority of the coal is within the nut-sizing range (13/16"-1-5/8"), but there are some bags with lots of nickel- and dime-size chips and some bags with lots of much larger chunks, sometimes up to what I would consider to be stove-size. I would imagine that pea would be mostly the nickel- and dime-size stuff (9/16"-13/16"). So a lot of what I've been burning could almost be considered a stove/nut/pea mix, I guess. I initially chalked the varying sizes up to breakage in the bags, but it seems to be more than just that. When one bag has a lot of larger chunks and another bag has lots of smaller chips, it's probably not just breakage.
Regardless, the nut seems to be burning just fine in my 503.