Hmm
Cons:
Poisonous
Potentially kill Brutus
Cost of keeping frogs ($10-20 per week=$520-$1K per year)
Potentially introduce parasites into aquarium and possibly kill other fish
Frogs grow slow take 3 years to get to decent size=3K
Inhumane IMO
Most expensive option to feed arowana
They'll eat each other
They take up a lot of room to keep (were talking 50L per frog=3000L tank=$$$)
Pros:
Arowana gets a variation from the normal
I don't get it as well :dunno:
Edit
Also think about the pain of keeping the flies in. And the maintainence, if you don't keep it up they'll get sick=sick arowana. And also the frog doesn't die quickly, the arowana will bite it breaking it's bones, and munch the internal organs, then the arowana will swim around and not immediately eat it. :dunno: