Hi Scott,
You are a smart parent to research this prior to your trip - especially if your girls are a little timid.
I also remember ExtraTERRORestrial Alien Encounter and
Stitch's Great Escape! is along those same lines. Its theater of the mind in the round. The main chamber is the same and they still use the shoulder bars. I don't recommend this attraction for anyone who is claustrophobic. They use sound, air, water and smell (yes a stinky burp smell) effects. Just as in Alien Encounter, there are periods of complete darkness when Stitch escapes and is on the run. This attraction is supposed to take place prior to Lilo taking Stitch in as her pet. He is Experiment 626 and not as cute and cuddly as he is after some TLC from Lilo.
While I do think they tried to be a little more comical than in Alien Encounter, its still an attraction geared for big kids or older. I think younger kids may still be frightened. My 6 year old is a little timid too and I haven't taken him on it yet. I'll probably wait another couple of years before I do. Its just not worth him getting in there and being scared.
I have seen some videos on YouTube if you'd like to get a better feel for it before making your final decision. Wishing you many magical memories :-) Allison