Thanks for all the feedback and comments!
I'm posting this update to walk back a couple of my original comments. I've used the iCab app at least a half dozen more times since my original post. The speed graph issue I mentioned hasn't happened again and that was the one that really irked me. I don't miss the missing features as much as I thought I would, although I'd love to have a train brake slider. Swiping on the speed graph is actually pretty nice, although getting all the way to 0 (right at the edge of the screen) takes a little finesse.
Overall, I think the iCab experience is acceptable, even pretty good, and I think handing a visitor who's completely new to model trains an iPhone instead of a Cab-2 should help them feel like running trains is something they can actually do.
