Allow me to quote from the kit instructions in this regard. "The chassis of tank Pz Kpfw 38 (t) were used for creation of anti-tank self-propelled guns (SPG) - the easy machines armed with powerful anti-tank guns. In May 1942 they started the production of new tank hunter Sd.Kfz 138 (Panzerjaer 38(t) fur 7.5cm Pak 40/3). Its arms consisted of 75mm gun Pak 40//3 and 7.92mm MG-37(t) machine guns. The thickness of front armour was equal to 15mm. The ammunition supply consist of 38 rounds. The machine in weight of 10.8 tons had the maximal speed 47 km/h. The SPG is powered by 6-cylinder four-stroke diesel Praga AC engine. The engine power is 150 hp. The crew consist of four members, a radio operator, a gunner, a loader and a driver. In total it was manufactured 242 of tank hunters SdKfz 138. In 1944 it was appropriated the name 'Murder III'. Till the end of Second World War SPG on base of PzKpfw 38 (t) were intensively used on all fronts."  (Sic to the whole thing)

If you have seen any of the other kits based on the PzKpfw 38 (t), then you know that much of this kit is identical as far as the hull and running gear are concerned. Where things differ is on the gun, mount and shield. In this case that would be the 'C' sprue which contains the Pak 40/3 gun and the upper hull.

The kit is molded in a light grey  plastic with large ejector towers on the inside of the big pieces. Easy to remove and clean. Despite having gone through thousands of cycles, the hull sections are in very good condition with no flash, few bothersome ejector marks and little in the way of sink areas. The tracks are plastic and sectional so that you'll have long runs with single bits required to go over the front and rear sprockets. I could find no optional parts and it seems that all the bits are there so none need to be made by the builder. It also seems as if the gun is fixed and cannot be made to move in either elevation or azimuth.

UM's instructions are well done with 10 construction sequences. Color information is given with Humbrol references and generic names. Most of the colors are for the exterior of the tank with only a few notes on things like road wheels, the machine gun and various wooden bits that are attached to the outside (shovels and the like).  Markings are provided for three vehicles, all from 1943 including the 9th Panzer Division and 23rd Panzer division vehicles in overall Desert Yellow. The third from the 1st SS Panzer division is in what I guess is overall Panzer Grey as the shade is not referenced. On the back of the box is a nice color three view of one in Desert Yellow with Dark Green patches. Decals are fairly well done, very matte and with large clear carrier. It seems as if there are markings on the sheet that are not used on this kit so you have some spares.