The only problem I have with a fishless cycle is: When do you know how many dead prawns has the same "bio load" as the fish that you intend to add?
Every time you add a fish, a fish dies, leaves on a plant dies, algae dies or you do a water change there will be a change in "bio load" and the tank will need to adjust (and it will). I therefore cannot see why people seem to get so stressed out about using fish to cycle their tanks. I think the pet shops are on to a winner with additives again. But that is only my opinion. You may well be causing more stress to your fish by doing a fishless cycle--who knows.