Yeah, that was a bit cavalier for something that had never been tested on something living. Then again, "That would have worked if you hadn't stopped me".
My problem is in relation to it being Garakkas plan in the first place. Once he's out of the brass room, he can control and communicate with ghosts to a limited degree from inside the ball. He gets deposited at the research facility, and finds out about the ghost extractor the same time as the audience. Now was that before or after Phoebe met Melody? When did Garakka recruit Melody? How did he know it would work the way it did (with Phoebe's mouth still being able to talk)? also Phoebe jumped to "I'll become a temporarily become a ghost" really fast.
I expected the recording that Podcast made of the record cylinder to come back into play, but it didn't.
They could have done with a few more drafts on the script to tighten up the plot and pace. Venkman and Janine were completely surplus to requirement and only there to get the old fans back for a bit of fan service.
You could even say the same for Winston as his new lab and Techs didn't really do anything to solve the problem, if anything they caused the release of the bad guy thanks to the tech they created at the new facility.
Even Mike wasn't integral to the plot.
There were scenes where people were just standing around in a scene with nothing to do.
I paid my money, I gave it a chance, but for me the story wasn't great.