Unfortunately, the Dunlop DVP4 Volume (X) Mini won't be shipping until May. Maybe someone tried it at the Winter NAMM show in January and can chime in. Musik Messe in Europe starts today, so there might be some feedback forthcoming from that trade show.
Here's a few possibly relevant things that I've noted, or (in the case of number three) have experienced myself thus far:
1) The DVP4 is more flexible than the FV-30H, with an aux output jack that can function as either a tuner out or an expression pedal out.
2) The DVP4 is $20 more at MAP than the FV-30H.
3) The DVP4 has an older and bigger brother named the DVP3 that I own. The DVP3 has a smoother sweep for volume swells than the FV-30H.*
*I performed a side by side comparison, and this was my finding. However, at this point I have no way of knowing if the DVP4 will do the same.