From Hsu webpage for VTF2-MK4:
The only Hsu sub I know of that has been measured in both sealed and ported mode is the VTF-15H and the impulse response shows that sealed has better transient response:
SEALED
PORTED
It should also be pointed out that with the large size of the Hsu VTF2-MK4 cabinet (which is a ported sub adapted to add sealed option), the full benefits realized by a sub designed to be sealed from the start are not realized.
An example of "designed to be sealed" vs "designed to be ported" on the identical budgets is the SVS SB1000 vs the PB1000 which both sell for $500:
SEALED
PORTED
Maybe, but it is atypical for a ported to be as tight as a sealed.