I have to agree with Robert. He did an excellent job articulating the experience with MTH 3e+ (Marklin) models.
I also love the MTH for Marklin models. They have great detail, good decoders, and provide an excellent way to expand US motive power on a Marklin system by loco type and road name. They also MU extremely well, even GP35s and F3s will MU together well. I would not hesitate to recommend them, but they are not without occasional flaw.
Keep in mind that MTH challengers may cost less, but also require 18" curves (R3 are 20.28", although I wonder if one could get away with R2 curves at 17.20"? ). Marklin locos (Big Boy, Challenger, etc) all run as small as R1.
Out of 10 MTH locomotives in my fleet, two have required return trips to MTH for repair out of the box. These were repaired free under warranty, and with no hassle from MTH, but it does take some time. Also, MTH locomotives run fairly well, but they are more prone to derailing. Sometimes if the track is dirty and a locomotive hits a dead spot, the following unit will push the lead unit into derailment over a turnout or vice versa. The GP35 units, if they loose power, will loose sound and lights unless you stop the locomotive, and begin the startup sequence again (I assume due to decoder fw, the F3 units do not do this).
I know others have different experiences, but I have found Marklin units to be very difficult to derail. If Marklin offers the same unit as MTH, I would always personally prefer to purchase the Marklin version. Without debating on motor type, I would be willing to guess that it would be easier to repair a Marklin unit in 15 years time than an MTH unit.
I am too encouraged by this new US prototype. Hopefully more will come in the future, EMD GP7s/GP9s or the SD versions would be welcome additions :) As others have mentioned, there were other Challengers, including Clinchfield, D&H, D&RGW, GN, NP, SP&S, UP, and WP. Not all were the same design, but it certainly provides Marklin with some future release options. Maybe we'll also see some UP passenger cars someday? :)
Regarding the smoke, I suspect there is a loss in translation. I would guess the contacts are on all the time during analog operation, but digitially controlled on/off during digital operation. I do think at this price that the smoke units should be included, but perhaps I expect too much?
-Brandon