i just got my Shredhead (SH) yesterday and here's my take on it...
equipment used:
-fender std. strat
-marshall MG15
the SH pretty much resembles the MI Audio Crunch Box (cbox) as per design (i had a cbox before btw).
that being the case, it has that fat ballsy sound matched with lots of gain.
but this is where the fun/value-for-money starts which i consider major improvements:
1) the SH cleans up pretty well---the cbox doesn't do that at all!
2) SH is fairly quiet even when gain is past 12 o'clock. you get a lot of hum from the cbox at these levels already.
3) presence knob - IMHO, this makes the difference. it is very interactive with the tone knob. the cbox gets too bassy making your tone muddy in most settings. this--fixes that.
in summary, mark explicitly mentioned that the SH is an improved cbox---IT IS!
i find it more useful as it is more tweakable.
kudos mark!