The 50mm if fired from above and at enough of an angle should be able to kill some of the lighter tanks (maybe) if you punch through the thinner upper armor. That wouldn't be unrealistic at all. It's just like the NS37 on the YakT can, and just like the 75mm on the B-25H can. It wasn't meant to, but if you do it right you can get a kill.
I haven't pulled up the numbers but I would imagine it is mostly useless against panthers, tigers, T-34s, and probably the firefly. Those seem to be rather heavily armored.
I don't think it would be the first tank killer choice, what with the IL2, the Hurr2D, and the Stuka cookie being better suited for that task.