I recently bought one for use with ProAc Studio 150's and have been very pleased. I've never had another sub so can't give you any useful comparisons but after a little experimentation with the placement, gain and crossover I feel like I'm getting all the advantages of the ProAc midrange and treble but with just enough added weight to make it seem like a significant upgrade.
The trick was to keep dialing down the gain until the sense of having the sub there disappeared into the music, something that happened at much lower volume from the sub than I would have imagined.
I bought a used but mint-condition VTF-2 here on Audiogon and it was easily worth the money. They're inexpensive enough and easy to resell so I definitely recommend it as an experiment.
The trick was to keep dialing down the gain until the sense of having the sub there disappeared into the music, something that happened at much lower volume from the sub than I would have imagined.
I bought a used but mint-condition VTF-2 here on Audiogon and it was easily worth the money. They're inexpensive enough and easy to resell so I definitely recommend it as an experiment.