An STF-2 is basically a VTF-2 in max extension mode.

An STF-3 is basically a VTF-3 in max output mode. The STF-3 can be ordered in max extension mode for $50 more.

Given the current sales, I think it's a great deal to order an STF sub. It sounds like there will be sales on higher ticket items soon. There was mention of getting two STF-3's in max extension mode for $1k. Maybe there will be a VTF-3HO sale too.

I"ve never listened to your Velodyne, so I can't comment on relative performance. I'd pick up an STF-3, but I'm already a Hsu owner, so I'm biased.