I was splitting these with a friend and ended up buying a new pair of mk21's without the HF boost. The way I saw it was, I'd rather have exactly what I wanted and spend a little extra now, than get the cheaper ones and always wish I had gotten the reg. 21s. My share was about $160 more to get the new fully warranteed ones.
Also, everything I read on the 21h's led me to believe that they were not made for our application.
I won't get to use them for a while, but I'll report once I do!