I've got two! LOVE them! Not sure of the V's but they're great! I've used them with regular 510 attys and carts, mega empty cartos (my favorite so far), and mega attys and carts (having some issues with this combo, but getting better thanks to some help here).
Liberty Flights has them, as do many other sites. You might want to shop around the Forum Suppliers and see who's got the best "sale/discount" going when you want to order. Liberty Flights has a 20% off sale right now....just go to the site and click the 20% discount in the upper left corner. The end price is pretty hard to beat!