Pneumatic props have their place but nothing replaces an actor. If you do not have actors you do not have a haunt. Pneumatic props have their place though.
Some are great eye candy, some can get startle scares, and most are great diversions for the actors to get their scares. We have not had many issues with the props breaking.
Maybe we are lucky- I'm not sure. We did have a solenoid fail on one and a mechanical failure (bolt) on the armature of another. Nothing too major.
I think they are great to have and I also think a lot of guests expect to see them at a haunted attraction. I am sure others will weigh in as well.