All skills work in PVP as described, so yes, even critical, power, or invincible turrets work in PVP.
Now to break it down for you... ALMOST EVERY TURRET IS USELESS IN PVP. This is coming from my experience as a level 112 Meister who rarely relied on turrets. Turrets are often used by runners or people who spam fire turrets and duck in a corner. In other words, get turrets if you don't plan on really fighting - but you still want to win anyway.
The only turret that keeps it's value in and out of PVP is a Push Turret. A Push Turret can push enemies off you in PVE, allowing you more time to run, pot up, attack, etc. In PVP, it allows you to KB your enemy or force them into a corner. The Push Turret, as well as any other meister skill, can be used mid-combo to halt the combo. This is very useful if the foe gets behind you or if the foe is running away. The Push Turret also foil Bladers' little plans when they try to use the "uppercut/hit/run/wait till they can use uppercut again" shtick.
The Slow Turret is another decent turret, but it's only useful in PVP since it cuts anyone's speed down to zero or less for a few seconds. This is great for really speedy opponents such as Wind Sorcerers or Treasure Hunters/Gunslingers... But other than that, it's useless. I never used it much, and found hitting a runner in the back with Meisteren/Gaiborg/etc to be more effective than spamming Slow Turrets.
As for the Power/Critical/Invincible Turrets... Those are decent, but they require for you to spam them to get the (better) effects of them. You also have to stick around the turret - and no person in their right mind would come running towards a Meister who's camping. I think other misc skills would be better than getting either of those turrets. Perhaps the Critical Turret would be good since you can keep the 30% crit damage buff, but that's about it.
"He who fights and runs away, lives to fight another day!"
Last edited by LilPhenyl; 02-24-2010 at 02:23 PM.