Not sure about the RO part....but IMO, ammonia in an established well planted tank, should get eaten up very quickly by plants. Maybe the reason why you see and explosive growth when you first use AS.
Both Jeff Senske and myself seem to think so.
If you follow the plan that ADA suggest, then you definitely will.
If lower KH is something you want to do, use peat in the filter, that's what's happening with the ADA AS.
They have been doing this for a good 50 years or more in the hobby, but you do not see the same types of benefits.
The control for the NH4 burst is zeolite.
That just addresses the NH4 in the water column, not the substrate.
I've not seen much differences using the zeolite.
So I'd say it's from the form of the N and the location for some plants.
If you make a non limiting water column, then you can rule out NH4 vs NO3 there.
At least you can test that effectively.