I wonder if MTH is confusing the MRC Pure Power Dual with the older MRC "Dual Power 027"? The older unit was a chopped-sine-wave (triac controlled) power source.
I selected the MTH Z-4000 because of the number of units I see running all day on the large modular layouts at train shows. Reliability, sine-wave output and remote control capability were important considerations for me. I have no regrets! I think the MRC Pure Power Dual is also a good unit, however.