I don’t know much about the bells and whistles, but back in college I did an internship at an explosives R&D company. One of the projects I worked on was low vulnerability tank ammunition. I learned really a lot about tank ammo and tank armor. It is a surprisingly complex topic. The details are a bit foggy, but I still remember the basic principles. I am far from an expert, but I predict these T-55s will last up to several minutes vs. any NATO anti-tank weapon and probably not much longer verses standard Ukrainian T-72s.
Since the dawn of tanks themselves, there has been a race to equip tanks with more armor, and then develop bigger guns to defeat that armor. The 55/54’s gun isn’t powerful enough to defeat any NATO tank. It still could have a role in infantry support, however. But the T-55’s armor straight up isn’t thick enough or sophisticated enough to defeat any NATO anti-tank weapons.
The T-55 in the photo’s amor has been partially upgraded with explosive reactive armor, which can be effective. As the name suggests, ERA explodes when struck by an enemy round. This helps prevent armor penetration by dispersing the round’s energy away from the armor. But many modern anti-tank weapons like the Javelin have a two stage warhead. The first stage detonates the ERA leaving the second stage to penetrate the armor. So even the ERA upgrade (assuming they even have that much ERA) won’t be much help. Exploding ERA is very unpleasant for nearby infantry so it isn’t used on western tanks.
Philosophically, it is an interesting question if it makes sense to use a $250K Javelin to destroy a $29.95 T-55. But I think the main takeaway is that Russia down to using disposable armor on the battlefield. A desperation move because they don’t have anything else.