In particular the 2/3 rail A4 Locomotive and how simple it is to switch between 2 and 3 rail running. I have 2/3 rail coarse scale models by Ace, Darstaed
, Basset Lowke (CORGI) and ETS locomotives and they all seem really simple to switch between 2 and 3 rail running compared to Seven Mills models which seem to be incredibly fiddly and frustrating by comparison