G Scale Comparison
The S-4 on the Gauge 1 track (left), and the S-1 on the Gauge 3 track (right).
The 1/29 scale Alco S-4 is not "G scale", it simply runs on the "G gauge" track made popular by LGB, some 30 years ago.
The USA Trains S-4 is a very nice quality, smooth runner. It's just a smaller scale that G scale.