No, it would draw 512 EU from the MFSU every 4 ticks, and every tick send 128 EU to the machine. This I am sure about (I have such setup). There is an internal buffer in transformers, I don't know how large it is, but it is at least as large as their input packet size.That's a good point, what happens if you convert 512 to 128 and the machine only needs 128 per tick. Every tick would it draw 512 from the MFSU for something only using 128?
This is my understanding of how they work: The transformer will first pull 512 EU from the input side and store it. if any machine connected to any of the output sides demands energy, it will send it from the internal buffer in 128 EU packets - but will happily send more packets at once for up to 512 EU/t. Once the internal buffer is empty, it will ask for another 512 EU from the input.