I don't think they are much of a biofilter- and there are much better choices for that out there, like Keeper mentions, the sponges could be all you need. They provide excellent biomedia.
Anything that removes ammonia is going to work against you when you are trying to cycle a tank, since the nitrifying bacteria require ammonia to survive. The only time I would use it is if there was a crash of my tank from a bio-overload or medication use, or something, and I had to pronto get ammonia out of there to save the fish. Water changes would do the same thing. In order to get the tank cycled again you would have to remove the ammo-chips.
I hope I am not confusing you - maybe I misunderstood your original post.