As of recently, you might have already known that PUBG nerfed all ARs damage as well as giving SMGs a slight buff in damage. That means SMGs are now actually a real advantage over ARs in close range now. But why the Vector? If you take a look here at this chart, you can see that Vector and Micro Uzi is now among the top auto guns that deal the most damage, just behind special weapons in airdrops and the Beryl.
Although the Micro Uzi was buffed with the Red Dot and Hologram recently, it is still not as good as the Vector in term of both damage and attachment.
The Vector has 5 attachment slots. The most important one that you would want to have is the Extended Mag or better as it initially has a rather small magazine capacity of 19 rounds. An Extended Mag will boost this number to 33 rounds which is a must for later phases. Other than that, it would be great if you can also find a Tactical Stock, a grip, and a muzzle to further reduce your already low recoil (preferably the Vertical Grip and Compensator).
Other than the damage output, as an SMG, The Vector allows you to move faster as well as go into ADS mode faster than ARs with better accuracy while hip firing. In addition, the Vector is now using 9 mm bullet, which is the most common type of bullets in PUBG at the moment. However, the Vector is only effective in less than 70 m range so it best for you to use a DMR as the secondary weapon to finish off the opponent.
Needless to say, the Vector is obviously perfect for Sanhok as the map is small and most combat situations happen in close to mid range.
All in all, if you are still wondering, Why don't you just hop into a match right now to see for yourself.