I didn't realize you were in India! That certainly increases the shipping costs
The HSU VTF-2 MK3 and Rythmik FV12 are not vastly different. I personally think that the FV12 is a little bit better, but not so much that it is worth any sort of big difference in price once you include shipping.
See if you can get a complete quote (price of the sub + shipping) from both HSU and Rythmik and go with the less expensive one! If it turns out that they are really close, then I would recommend the FV12 a little bit more highly. But if the HSU VTF-2 MK3 is a fair bit cheaper once shipping is included, you'd be giving up very little in terms of performance.
If you want a really rough idea (and I stress ROUGH idea) of the sort of sound quality and extension that you can expect, have a listen to a Velodyne DLS-4000R and/or a Velodyne DEQ-12R. Those are the most comparable, although I personally think that the Rythmik FV12 sounds better than the DEQ-12R and plays a little bit lower too.
That said, if you can buy the Velodyne subs locally, the price difference might be pretty big when you don't have to pay any shipping. Like I said, get full quotes from HSU and Rythmik. Then compare those prices to what you could get a Velodyne DLS-4000R or DEQ-12R for. If the prices all wind up really close, I'd still say to go with the Rythmik FV12. But the Velodyne subs have some nice features with built-in EQ and whatnot and they are good performers. Being able to buy them locally might mean that they cost substantially less than shipping over an HSU or Rythmik, so they'd be well worth your time to consider, IMO
