it's a case of reding between the lines a bit here, it's actually fine to use it.
some water companies use a chemical called 'chloramine' instead of (or as well as) chlorine, chloramine is made up of chlorine and ammonia and to get rid of the chlorine element you need to split the two chemicals apart, so the dechlor does this and then works on the chlorine and gets rid of it as it would with normal chlorinated water, but you're then left with a small amount of 'excess' ammonia in the water so some products will also neutralise this. Now they don't actually get rid of ammonia either, they convert it to ammonium which can still be used by the bacteria in the filter but is not dangerous to fish like ammonia is.
so all it's actually saying is it converts the little bit of extra ammonia from the chloramine bond into ammonium, but that's not quite as snappy a claim and a lot of aquarists just wouldn't understand it but know that ammonia is bad so anything that gets rid of it is good.
so in teh quantities you're using it's not going to get rid of the ammonia that you add to do a fishless cycle or any other significant amount of ammonia in either the tap or tank water. And even if it was to work on some of it then it's no bad thing anyway as the filter bacteria can still use it.
