Don't know about the alternators on airheads, but I'd never go for underpowered permanent magnet alternators.

In my use there's:

Headlights: 2x50W=100W
2 heated vests for me and g/f: 2x75W=150W

Add the consumptions of battery recharging, bike starting, ignition, EFI, (ABS if you have one), standard heated grips on BMWs, the rest of lights and gizmos if you have and you're already exceeding 450W alternator which is already considered very high output in permanent magnet alternators field on motorbikes and needs around 5000rpms to produce it. Normally they're around 300-400W max, presumably around 300W or less average because you aren't revving your boxer over 5000rpms most of the time.

My R1100GS stock brushed alternator does 700W which is sufficent for my needs with a bit of reserve and creates 70-80% of it already from 2000rpm or so.

Never replaced anything on two bikes done over 120,000kms, not even the alternator belt that has service interval of 60,000km. So it needs very little maintanance. I do lot of offroad and bad roads here. On travels just in case I carry alternator belt with me that takes very little space and costs little.

Yeah, someday you have to replace the belt, and pulleys + brushes too in more extreme usage, but it's a dead easy job and costs very little.

Considering the surprisingly big amount of problems I've seen with permanent magnet alternators on offroad/big trailie oriented bikes (normally the magnets get cracked because of bike taking constanty bumps, vibrations on bad roads and also bigger output alternators tend to have bigger magnets - more mass makes it more vulnerable to bumps or gyroscopic forces and the magnetic materials used in the alternators aren't exacly very resistant ones), then in my point of view looks like permanent magnet alternator isn't always justified compared to more powerful brushed alternator, especially if you have above average wattage needs like I do (i.e. heated vests, a bit more powerful headlights).

So if you need relatively healthy amount of power, there's no real escape from brushed alternators anyways.

Thus figure out your needs first.