Here are a couple clips which demonstrate each using the same MIDI file:
There are a lot of different kit pieces to choose from for each kit, plus also different mixer presets (which involve more or less effects too). These were done with the default kit pieces and "original mix" mixer presets. So it doesn't speak for the versatility of either, or whether you'd like more pieces in one kit vs. the other. But I feel it does sum up the general difference between the two in terms of what realm each one covers. Metal Machine is more snappy/in your face, Made of Metal is more warm/less produced (maybe "more realistic production", and "more room to produce the sound yourself").
Then again, Made of Metal has some presets that sound more "produced" and "in your face" too. I've uploaded a second clip of that kit here:
It's still less "snappy" and "produced"/"tight", but it's a more "in your face" preset with different kit pieces chosen as well as a different mix approach.
I hope that helps!
My recommendation is to get both.