Never used it so I can't speak from experience. Soy can cause intestinal inflammation in various fish species according to studies-- some species more sensitive to this than others-- and you might find thisinteresting regarding the problem with a soy/pea combination. Effects can also vary with form and processing of soy and I don't know how much the term "soy protein" in their ingredients really tells you about the exact form or processing. I suspect, since most people aren't aware that some food combinations might cause digestive/intestinal problems in fish, it's inevitable that at least some would misdiagnose or come to erroneous conclusions about the real cause of some health issues.
Anyway, my personal preference is simply not to use foods with soy in them, but that's just me. There's a lot of such foods out there and a lot of variables.