Indeed, the M57 takes a different (harder to find, and more expensive) magazine than the standard TT-33 that holds one more round. Can't use standard Tokarev mags in an M57.
Additionally, the M57 has a full-length guide rod (unlike the TT-33), which in theory has something to do with increasing reliability (although the TT-33 is an extremely reliable gun as it is), in practice all it does is make it slightly harder to reassemble, much like full-length guide rods do with 1911 variants, although at least the guide rod is jointed to assist in reassembly.
Another functional difference is that many of the M57's actually have a factory thumb safety, unlike the TT-33's which relied on the half cock notch as a safety and are modified with an additional thumb safety in order to be imported into the USA.
Lastly, the way the firing pin retained in the slide differs noticeably between the TT-33 and the M57 and neither is particularly pleasant to disassemble and especially reassemble without the right tools, but not bad otherwise. You will have to do this if you buy a gun that hasn't been scrubbed free of cosmoline.
Aside from that, there's minor aesthetic differences, such as the size of the mag release button.
