These models are available in three different permutations - Original, Modern, and Final Rebuild. And although released in the same year as PRB's ill-fated 4-8-4 Niagara, the mechanism employed in these models is vastly superior to the one employed in said Niagara.
As is generally the case with brass steamers, the metal chassis is fairly minimalistic (with most of the model's weight provided by the shell). The motor is a cheap looking five-pole / straight-wound open-sider. Right-rail current is collected by the pilot truck, the trailing truck, and two of the right-side drivers (the center drivers being equipped with traction tires). Left-rail current is collected by the six left-side tender wheels and transferred to the engine by way of a stiff wire on the tender drawbar.
The motor and worm box are mounted on a torque arm that is equipped with a leaf spring. The motor driveshaft and worm shaft are joined by a pair of hard plastic sleeves. Only the center driver set is geared. And since the gears are basically inaccessable, I can't say whether they're metal or plastic. Each axle has a set of bearing blocks where it mounts to the chassis. There is no lighting. The pilot truck is sprung, and the pilot itself is equipped with a semi-operational knuckle coupler (IE, it does pivot - however, given its small size, I'm not sure how practical it might be). The tender does not come with a coupler, although a Micro-Trains friendly mount is provided. Wheels are low-profile, so no problems on Code-55 rails.
As delivered, performance is pretty poor. And as is usually the case, the culprit is that stiff wire on the tender drawbar. Out of the box, mine was unable to maintain any kind of consistant speed. Worse still, it would constantly stall out at anything less than full throttle. The problem here is that the drawbar wire is mounted too loosely to the drawbar, and the end result is iffy conductivity between engine and tender. Fortunately, the solution is an easy one - simply apply a bit of solder to the wire where it connects to the drawbar (to stiffen up the connection) and all of the electrical problems magically go away.
After applying said fix, my 4-6-4 ran virtually flawlessly - whisper quiet, smooth throttle response, excellent slow speed creep, no problems with any of the wheels derailing, no problems on narrow radius curves, etc. And although I didn't go so far as to actually stick a coupler on the tender, given the traction tires on the drivers, I'm assuming that pulling power is going to be adequate. OK, the top-end speed is quite excessive. But apart from that minor nitpick, the only other problem I noted with mine was a very slight wobble (only really noticeable at high speeds). Beyond that, this is a very nice looking model that (once the drawbar situation has been addressed)) runs quite well. No, not quite "Kato Mikado" well, but definitely right up there.
To remove the locomotive shell, unscrew the two small screws on the back of the cab. Then, unscrew the pilot truck. The shell should lift right off at that point.
Grade: C (A with the drawbar modified)