I honestly don't know if there's any difference at all, but yeah it's the newer 400 series. The MH and H series are so freakin beatiful.
I loved the H-300 (with the old cockstock) but the only one I found used was already sold.. and as I said I hate the abalone stuff so I went with the MH in the end. What guitar did you get instead?
i prefer the standard ESP headstock, for me one of the best
but the headstock on the H-300 isn't bad also,
looks similar to the headstock of my regius, which replaced the MH-400.
here's a link MAYONES REGIUS 6 i've got exactly this one but with a EMG 81/60 set
cheers
S.