Rumble filter and limiter are on different principles. Rumble filters actually filter out low frequency signal. It is necessary for vented sub because below the tuning frequency, the driver becomes "unloaded" (meaning there is no enclosure back pressure to limit the excursion). So rumble filter is like a guard at the gate checking everyone's ID. But even with that, the club can still be over-crowded. So limiter is like a volume control on the fly that "shrink" the signal when it thinks it is about to go into clipping (like shrink the people in the club so that it can accommodate more). Rumble filter still follow linear operation. Limiter does not. That is the first difference. Second, rumble filter is necessary for vented subs, but not for sealed subs because sealed subs have enclosure back pressure to keep the excursion in check. Third, in sealed subs, one can use rumble filter to conserve energy (or power) so that it can be used on more audible frequency band.
FV15HP vs F15HP: F15HP has better bass extension. But its 20hz output is not as good as FV15HP. It is 10hz max output is roughly 12db down from 20hz and it is 5hz max output is roughly 24db down. On the other hand, FV15HP in 2port mode starts roll off at 18hz. when it reaches 9hz, its max output already about 24db down. At 4.5hz, its output 48db down. 1 port mode improves the output down to 13hz. But below that, its roll-off characteristic is just like 2 port mode. So the lower it goes, the less output it has compared to F15HP. So even though F15HP may start with less output at 20hz, but as the signal moves lower in freuqency, it begins to show its advantage over FV15HP. But the most important part is how you trade-off the two.
Any of the following situation would warrant an FV15HP over F15HP:
1) You are happy with the sound of your current vented sub and just want to improve the tightness and overall realism (vs some customers absolutely don't like vented subs).
2) You prefer more full body sound. You have listened to some sealed subs and they are too lean for your preference.
3) You use the sub for 90% HT. You are not really that critical about the music.
4) You used to have a sealed sub, but the vented sub in your friend's house blows your mind.
Any of following situations would warrant an F15HP over FV15HP:
1) You are happy with the sound of your current sealed sub and just want to improve the extension and overall realism.
2) You like fast, clear, and articulate sound. You don't really play loud and your system seems to have high resolution that you can hear the sound from different components (such as different power amp, CD player, cable, ....).
3) You have a more acute hearing than others. You consider yourself to be a more musical person than average.
4) You are all of the above except you do play loud which will require multiple sealed subs.
5) You used to have a vented sub, but you heard a sealed sub in your friend's house and it blows your mind.
For those still cannot decide, either one will do
Feel free to add as the above is just a general guideline. If we get enough consensus, we will put that on the web.