To those of us who love link and length tracks, but are tired of assembling them, cometh Modell Trans.
Their solution for the UM Pz38(t) range ? A simple, pre-assembled, finely cast, drop-in replacement set to which only the outer halves of the idler and drive sprocket have to be added.

Comparison of original UM track assembly (top) with Modell Trans parts (bottom).

The main advantage is obvious: it allows for extremely fast assembly, more so as the wheels are perfectly aligned with the stubs on the UM hull.
The fit with respect to the UM kit is so good that you don't need to use glue. This allows you to keep the running gear as a subassembly, which eases painting.
Extremely fast, I said ? Well, yes, you don't need to assemble the tracks, but there is some work ahead cleaning the flash beneath the wheels, which will take quite some time to do right.

Modell Trans parts after clean-up

Alignment of the individual tracks links is not always perfect, and Modell Trans followed the UM instructions which will have you install the tracks backwards.
Another disadvantage is that you cannot control the sag. (Not that the sag given by Modell Trans is unrealistic, but I like mine just a bit more pronounced.)

Not immediately obvious to the casual observer is the fact that Modell Trans improved the roadwheels, and this is one of the more convincing points of this set. They have improved the rim, or better they added a rim, and thinned the thickness of the rubber tyres, which is overscale in the UM kits. The hub detail has also been improved. Idler and drive sprocket remain unaltered.

Note that this set will also work for the rear-engined Marders (e.g. this one) and rear-engined Bisons derived from the Pz 38(t) (which keep the two return rollers), but not for the mid-engined variants (which only had one return roller) nor for the Hetzer.