Hi Phill,
You touch on an interesting point: "realism". To many in the G1 fraternity, close fidelity to the prototype (even the scale) are of secondary importance. To them, a steam loco is more realistic if powered by steam, even if it does not compare brilliantly to the prototype (I am aware that Aster buck the trend here, but I am thinking more of the builders rather than the buyers). I agree that an electrically powered model with decent sound effects and maybe a smoke unit would more closely resemble the look and sound of the prototype, but that is, to attempt to draw a distinction, a model railway approach. To a model engineer, this is often not the approach taken, and to be honest they can be a bit snobby about it, with potential for amusing conversations.
As an example, the late and great Nick Dillon once commented to me that he didn't think much of the SM32 crowd, because they used externally fired locos (even most gas burners with a "centre-flue" boiler are externally fired, as the exhaust is not required to draw the fire) and the locos had bowdlerised valve gear that didn't allow notching up, whereas most G1 locos were more realistic as being internally fired, you had to learn to drive them. I innocently asked how many prototypes were fired by methylated spirits, and required to be push for two revolutions of the drivers to change direction - and pointed out that slip-eccentric locos aren't usually notched up, either. He was a practical man and prepared to concede the point. I did, and still do, agree with him, though, that an internally fired loco where you have to learn to balance regulator, water bypass, fuel rate and so on is more challenging, closer to the real thing in many ways, and more fun. The interesting point is that SM32 grew from being much, much smaller than G1 to a lot bigger, and a lot more affordable, precisely because externally fired locos produce steam at a constant rate and allow one to sit back and enjoy the running.
It all goes back to realism - for me, SM32 and G1 steam is spoilt by the "tick-tick-tick" rather than something more bassy and resonant, and whilst the
Summerlands Chuffer goes someway to addressing this, it isn't really enough. Mind you, there is room for a really big bass speaker in most G1 tenders and diesel bodies...
To me, the big advantage of G1 is that it has the potential to be the meeting point of model railways and model engineering, although I suspect that G3 is delivering more on this front.