Parry Knife Questions

So i picked this little guy up at sl27 and wanted to try it out. Im running a dex build with bandits knife atm.

Now i have a questions, after playing with it a bit MYSELF i find it SO much fun once you get the feel of no shield.

QUestions: How is the knife in pvp? And Pve? (used in my left hand of course)
Does upgrading it increase anything of interest if i dont want to use it as an attacking weapon?

To answer your questions, the knife is fantastic in pve when you get the timing down. Now as far as parrying in PvP goes, thats a different story. The bonus the knife has is a longer window to riposte, this comes at the cost of the speed of the actual parry. If you have the timing of the knife down you are still not guaranteed to parry in pvp because of lag. With bare fists and light shields I can parry about 60% of the time, landing the riposte maybe 40% of the time. It all comes down to practicality and whether or not you want to make a character that is good at pvp, or a challenge to fight with. I can tell you from experience the second is much more frustrating but much more rewarding to win with. As for upgrading it that does not effect it at all if you don't use it to attack. I would still recommend upgrading it. Having an off hand weapon can be great to quickly stun an unarmored player to set yourself up to do a strong attack with your main weapon.