old topic i know, but i thought i'd add my two cents.
yesterday i did the swap from Amquel+ to Prime. there is one thing i noticed that Amquel+ does a hell of a lot faster.
i have a 29 gallon freshwater tank that's in the process of cycling. as a result, my nitrite levels are around 2ppm. now, when i wanted to reduce the nitrites and i added Amquel+, the nitrites would read 0ppm after about 30-45 minutes.
yesterday, like i said earlier, i made the transition and started using Prime instead. i'm pretty disappointed with it's nitrite nullifying performance compared to Amquel+. according to my testing using API's nitrite test kit, the stuff is either really slow or doesn't work very well in controlling nitrites. i even used 5x dosage allowed to treat nitrite emergencies, as per the directions on the bottle. even now, overnight, the nitrite levels haven't dropped down to zero, the way the Amquel+ did it; they're still at 1ppm.
this is by no means a scientific test, but just my experience with both products.