Why do you thnk Muzzy came out with the MX4?
Because the ST is such an exceptional broadhead.
So what is it about the ST that folks like better than the Muzzy's?
All steel one piece furrels, machined furrels, sharper blades, thicker blades, better flight characteristics, exact weight, ability to spin the lock washer and tune them to each arrow, stronger, more durable, etc...
Having said this the Myzzy is an excelent broadhead that will kill everything you shoot it at but it isn't what a ST is IMHO.