Yes, there are a number of criticisms one can level at the system, but I think that the adventure is perfectly adaptable to other sets of rules, I just decided to give it a try with the original Fringeworthy game.
Whilst not wanting to get into an elongated discussion about different systems I think your hands off approach to it appeared to make up for any over-crunchy rules. It was great to listen to theAethernauts again
EDITED TO CLARIFY: Regarding the slow combat and rolls - it is slow, but you can tap the screen and jump to the result of the roll rather than sit through the laborious animated maths
I recently kept my DnD group on their toes by trying them out on the Advanced Fighting Fantasy system. It worked well - they've never really been able to keep up with 3.5 - but the thing that I'd forgotten was the sluggish combat even with the advanced rules for damage. So it doesn't altogether surprise me that iPhone has the same problem