Video Slave allows for synchronized playback of clips with up to 60 frames per second. This will allow you to use it in all common situations in the current postproduction market (should there be a scenario we've missed, please drop us a message). MIDI timecode (MTC) - being a standard from the 80s - doesn't support frame rates higher than 30 frames per second.
To be able to play timelines with high FPS clips in sync to MTC, Video Slave will try to match the incoming TC at half the frame rate. If your timeline e.g. has a 50 fps clip, Video Slave will play it in sync if an MTC with 25 fps is supplied.
In the timeline list, the timeline frame rate is shown here: