I tried a -1.5 deg headset on my old orbea rallon, taking the angle from 66 to 64.5 deg, it was better downhill, but at the expense of less weight (and therefore grip) on the front wheel on the flat and uphill, in an ideal world I would have paired up the head angle change with 5mm longer on the chainstays, but thats not possible. It just felt a bit unbalanced with the angleset.
I did the same with an IBIS mojo HD – same end result as above.
So I’m a bit meh about anglesets, IME they do noticably and negatively affect the balance of the bikes I’ve tried them on.