I've never had a servitor turn on me while playing a conjurer. You make a circle to protect yourself in a situation where you fear a servitor turning on you. Also, you make a circle before trying to dismiss the servitor.

If you look conjurers by alignment from Battlefield, you'll see the following disribution:

Good 451
Evil 258
Neutral 151

Neutral conjie is a difficult choise, as both good and evil servitors are weaker than for the good and evil aligns, which do not bother to use the servitors of opposing alignment. As for tanking expectations, you can't expect to tank like a goodie conjurer, as the archon won't likely be as powerful and happy as it would be when summoned by a goodie conjurer. Evil conjurer too is more squishy than good, suffering from deaths to servitors more often than his good counterpart. People who have actually played a neutral conjurer probably know the difference better than I do, but being a bit paranoid can save you from eating a few servitor deaths.