This set is meant as a straightforward conversion project for a very interesting vehicle: a tank hunter produced in small numbers by the Soviet Union based on captured Panzer IIIs and armed with a S-1 gun (which is basically the same as the F-34 used in the T-34.)

According to my references about 200 were produced in 1943, most seemingly on a late Ausf.L or Ausf. M hull, i.e. without the lateral hull hatches, although some pictures show vehicles with the escape hatches.
The vehicle saw action at the battle of Kursk, after which it was slightly modified by adding a gun shield.
Some vehicles received a commander's cupola (also from the Panzer III), which required a slightly modified fighting compartment.

Although apparently successful, most were withdrawn from active service by the end of 1943; some soldiered on as training vehicles.

The Leva conversion kit will allow you to build a post-Kursk vehicle with gun shield and without commander's cupola. For those wanting to backdate the kit, carving away the gun shield will not be a difficult task.

You get 5 kit parts to accomplish this conversion, the boxy superstructure being the most important.
Some vehicles carried external fuel barrels, which the set does not include, so you might want to pillage the spare's box if you like the look of them.

Something that is not immediately obvious is that the driver's visor was moved outwards with respect to the ordinary Panzer III.
Compare the SU-76i with the Panzer III and pay attention to the deflector strip in front of the visor.

Casting is slightly rough, but probably accurate for Soviet wartime production practice. There are very few casting imperfections; the most noticeable being the bent gun barrel.
I am not sure if you can get it entirely straight after dipping in hot water (or heating it otherwise), so I would go for a replacement barrel. (You can use a gun barrel for an F-34.)

The set is meant for either the Esci, Revell or Matchbox kits. Given that the latter is 1/76, I am not sure how the fit will be, but for the Revell kit the dimensions are spot on, as the pictures below can attest. At any rate, I would recommend the Revell kit above the others, as it is by far the best currently available.

Note that some references claim that the Soviets removed all tools from the fenders. Given that most kits have the tools molded integrally with the fenders, this will be a pain to do. Then again, I see no point why the tools would have had to be removed.

Sources:

Trophies in the Red Army, Frontovaya Illustratsiya #1, 2000; M. Kolomiets, M. Svirin «Kurskaya Duga», ExPrint NV, 1998; «Poligon» #1, 2000.

http://www.battlefield.ru/en/tank-development/29-sp-guns/63-su76i.html

http://ww2armor.jexiste.fr/Files/Allies/Allies/1-Vehicles/USSR/6-SPG/SU-76(i)/SU-76(i).htm

http://ww2drawings.jexiste.fr/Files/1-Vehicles/Allies/2-USSR/06-SPG/SU-76i/SU-76i.htm

http://www.thetankmaster.com/english/afv/su-76i.asp

http://www.tanks-encyclopedia.com/ww2/soviet/soviet-su-76i.php

Review sample courtesy of Alain Levesque of Leva Productions.