The fact still remains that Albertos amps use a switching device nobody else can source. Again, one that was designed for Audio, not for a battery charger or DC power supply.
The only parameter that can make a GaNFET more suitable for audio is a low output capacitance. Other than that there's no way to optimize a GANFET for audio.
GaNFETs are designed for high power switching applications. While that might include a SMPS or battery charger, in such applications the cost of the output switching devices can play a pretty big role in the device used. So a battery charger is far more likely to use a MOSFET instead owing to an order of magnitude lower cost. GaNFETs are more likely to be motion control or other high power application (such as class D operation) where precision high efficiency/low noise switching is important.
Anecdote department only: we have more than just 3 customers that have compared the AGD to our amps and the result was the other way 'round (one of them commented above). In the end anyone will still have to try it out and see.
@srama I recommend a balanced preamp if you can. That's what we use here in the shop and what I use at home.