Small tank destroyer is small. I'd make some comment about how dubious of a design this thing is/was, but then I remembered we have the Scorpion...

Looking into its history, the ASU-57 was one of several design proposals for a "lightweight assault gun" (which by this point you'd probably get the same effect sticking a recoilless rifle onto a jeep), specifically for the airborne forces (again, jeep with recoilless rifle); prior to the ASU-57, there was the ASU-76, which was based off of the T-70 and was dropped because it was still too heavy to be airdropped despite the armor being only 3mm thick; and the K-73, which bore many similarities to the ASU-57 (both in shape and armament) but was also cancelled. Sometime afterwards (not sure how long), work on the project picked up again, with updated requirements, and it was at this point that the ASU-57 finally came to fruition.

Serving for over 20 years, the ASU-57 was, despite being basically an aluminum box on tracks, a (somewhat) successful vehicle which did see some combat outside of Europe, most notably by Egyptian forces in the Six-Day war. As its intended role, it probably was a step up from being deployed without any kind of heavy firepower, but was almost certainly outclassed by a majority of contemporary AFVs, be it due to having barely any armor and being open-topped, or due to the fact that the 57mm gun was effectively WWII-era tech that was having to compete against (at the time) modern weapons that could provide the same effect and then some, like the B-10 82mm recoilless rifle. Even the Scorpion, a similar vehicle in terms of general design, had an arguably better main armament despite being basically completely unarmored.

Besides its eventual replacement by the better-armed and fully-armored ASU-85, the ASU-57 did have some prototype variants that, while not able to see service (either due to funding issues or a general lack of interest by the military), did suggest that the Soviets were aware of the issues that the vehicle faced, and were making an effort to address said issues. Most notable of these prototypes was the BSU-11-57F/2T2, which carried a far more powerful 107mm recoilless rifle; this change in armament would've definitely increased the firepower of the vehicle, placing it on par with anything NATO had in the way of lightweight anti-tank/fire support vehicles. As things went however, the prototype did not appear to see much further development, likely due to development of the more powerful ASU-85 (more powerful compared to the existing ASU-57).

Honestly not my best writing; I can't tell if I am trying to praise or criticize this thing, and that's probably because it's one of those "successful" vehicles that weren't so successful because of certain elements of its design that just held it back from being as effective as its contemporaries were at this time. It doesn't help either that there isn't really a ton of information regarding service history; twenty years in the Soviet arm, maybe longer in wherever it was exported. That's about it, from the looks of it anyway. In any case, I hope you at least find this information vaguely interesting. Stay tuned for the next tank (should be found in my "roadmap" journal).