They do attach to the 'V' groove at the correct height on the MFT/3. I think they will work well as long as you are doing quite a few cuts at the same or similar size. If not the spacing between the extensions will need to be adjusted (which is pretty easy) in order to keep panels on the flat support area and not on top of the fence portion.
Are you also getting the Kapex MFT or going with the Kapex cart?
It may not look like it due to picture angle but the MFT/3 is at the height of the Kapex "deck" .
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Seth