The 4D M3 half-tracked armored vehicle (半履带装甲车) was released at the same time as the
4D Sd.Kfz. 7, but I overlooked it because in the initial listings I saw, it was not advertised as a 4D model, or as 1/72 scale.
The model is described as a M3 half-track on the box, but it is actually a
M21 Mortar Motor Carriage. It consists of 35 part in total, with 29 parts in green plastic (some parts are painted in black, and the national symbol is stenciled on the hull in white), the two front wheels in black plastic with hubs painted green to match the body, two vinyl tracks, a clear plastic windshield, and a metal axle.
The details of the kit are very rudimentary. Parts are thick and overly simplified. The engine louvers and roller wheels are particularly bad. I don't see an easy way to make the model into a M3 because the rear compartment is part of a single piece hull configured as a M21.
When putting the wheels on, align the drive sprockets, rear idler, and roller wheels so that the outside edges are flush, otherwise they will look misaligned when the tracks are in place.
I also had to file down the metal axle a bit so that the wheels did not stick out too far. The wheels need to be pushed in so they touch the chassis in order to be flush with the fenders.
The instructions tell you to add the tools before placing the hull on the chassis, but it is probably a better idea to add them after the hull is put in place. I had glued the tools in place, and found that the pins on the tools prevented the hull from going all the way down, making it necessary to clip off the ends of the pins before the hull could be seated properly.
Despite it's flaws, the model goes together quickly and looks fairly decent from a distance, though the windshield needs to be painted or the edges really stand out.
The size of the 4D model is nearly identical to the Forces of Valor M3A1.
I'm not sure how scale accurate the models are, but both are significantly smaller than Hasegawa, Corgi, and PSC half-tracks, which are all roughly the same size (probably ~1/70 scale).
One of these days, I'll have to dig out my Academy and Italeri M3 half-tracks and do a comprehensive size comparison of all the different models.